Fletcher Cox, now 30, has power and money. But this is a pivotal year in his Eagles career.

Age is only a number, and in the NFL the number for that aphorism is 30. No other age has as negative a connotation.

Fletcher Cox understands the context of turning 30, having done so six months ago, which is likely why he corrected the semantics of a recent question that opened with the phrase: You’re now entering your 30s …

“I’m not in my 30s. I’m only 30,” Cox said. “So let’s not make me older than I am.”

The Eagles defensive tackle added a chuckle at the end of his assertion, but for most players the big 3-0 isn’t a laughing matter. It takes a certain level of skill and devotion to last that long in the NFL, so it’s not as if teams view the age as an expiration date. Each case is its own.

But 30, or thereafter, is an oft-used benchmark for assessing decline. The NFL isn’t a league for old men. At the start of last season, players over 30 made up only 16% of rosters. The average age has been decreasing for years, and it’s often another number — one preceded by dollar signs — that has helped influence this trend.

Cox, though, has managed to avoid the fate of so many high-priced players his age. He is, of course, a franchise great, and has been given considerable clout as a result — too much, according to some Eagles staffers, past and present. (More on this below.) But his production slipped the last two seasons just as his salary peaks in the last two years of the $102.6 million, six-year extension he signed five years ago.

Cox’s cap number this season — approximately $24 million — would put most in peril. But because the Eagles kept restructuring his contract to serve their short-term objectives, he remains entrenched. Next year’s similar cap number offers a chance to alleviate some of the dead money, but not without a significant hit.

The mere mention of moving on from Cox, a six-time Pro Bowler with Hall of Fame potential, might sound preposterous. He is still arguably the Eagles’ best player. And he still has the ability to warrant the increase in his salary. When Cox is at his best, there might not be a more dominant interior lineman, and that includes Aaron Donald.

But Cox hasn’t been as consistent as the Rams’ defensive tackle, particularly the last two years. Injuries haven’t helped. Offseason foot surgery slowed him at the start of the 2019 season. A neck injury pestered him during the second half of 2020. To his credit, he missed only one game over that span.

There was a feeling among some coaches, however, that Cox wasn’t maximizing his ability over that span, or taking the necessary preventative steps in terms of his health, team sources said. And there is an internal concern that he won’t take the extra steps as he enters his 30s to retire in Philadelphia.

The Eagles aren’t tanking 2021, but they are a team in transition. Does Cox view himself as a veteran bridge to the brighter days — e.g. Brandon Graham and Jason Kelce — or as one of the centerpieces of that future? If it’s the latter, finishing out his contract or getting an extension could hinge on this season.

“I’m always looking forward to competing any time I’m on the field in practice, individually, just doing anything,” Cox said last week when asked how he would approach what could be viewed as the next phase of his career. “Making sure that my body is ready and to gear up for the next season.”

Cox often talks as if he doesn’t have a care in the football world, and in many ways he doesn’t. He’s long established his bona fides. He’s won a Super Bowl. He’s earned more money from the Eagles than any other player in franchise history. He could coast in his final years and still possibly end up in Canton.

But it isn’t a foregone conclusion, especially considering Cox’s recent regression, at least in terms of production. From 2015-18, he averaged eight sacks, 10 tackles for loss and 76 pressures per season. In the last two seasons, those averages have decreased to five sacks, seven tackles for loss and 52 pressures.

While too much emphasis can be placed on those statistics — there isn’t a metric for the number of times Cox was double teamed, for instance — even he has expressed dissatisfaction with his overall performance.

Typically, a mega-contract would be structured to account for a natural downturn. But Cox’s cap numbers are their largest in the last two years. The extension he signed still holds up. The $63.3 million guaranteed is the second highest among interior linemen — behind Donald’s $87 million — and his per-year average of $17.1 million is sixth.

The Eagles, as a result, have given Cox great leverage. But it isn’t just the contract that has given him sway in the NovaCare Complex. General manager Howie Roseman’s preferential treatment of star players, according to team sources, created a culture in which a select few could influence personnel and coaching decisions.

The Eagles, of course, aren’t alone among NFL teams in favoring franchise cornerstones. But Roseman’s emotional attachments and favoritism, sources said, have led to player power beyond the expected norms. And Cox, to no surprise, took advantage.

“Howie basically checks everything related to the defensive line with Fletcher to make sure it’s OK first,” a team source said. “So that has often led to certain people getting jobs, and in some cases, the same losing them.”

The Eagles and Cox, through a team spokesperson, declined to comment on the various claims made in this story.

Cox isn’t the lone reason why the Eagles have had four defensive line coaches since 2016. There have been myriad factors, more recently the hiring of a new head coach. But the defensive tackle’s sentiments did play a role in the departures of two assistants, team sources said.

Chris Wilson, who had coached Cox at Mississippi State, was hired in 2016. The Eagles had downplayed their prior relationship, but Roseman had gotten Cox’s blessing before the transaction.

The defensive line was arguably the strength of the team during Wilson’s three years in Philly. Roseman has poured significant resources into the unit for years, but there was little external criticism about the job Wilson had done during his tenure, which included a championship.

Cox would have arguably his best year in 2018 when he recorded a career-high 10½ sacks. But there was increasing tension between the player and coach, which reached a crescendo when the Eagles hosted the Texans in the penultimate game of the regular season.

The line had spent the week prior practicing on how to defend the mobile Deshaun Watson. But the Houston quarterback would run for 54 yards and two touchdowns, and often did so when the Eagles failed to contain him on the edges.

The Eagles eventually won, but when the film was reviewed the next day, Cox questioned how Wilson had prepared the group, sources present said. The coach declined to take responsibility for the results and there was a heated exchange.

An irate Cox then went to a support staffer’s office and asked him to call Jeffrey Lurie and tell him “to get rid of” Wilson or he would call the Eagles owner himself, sources close to the situation said. The call was made, but mostly to de-escalate the situation.

Cox wasn’t the only player frustrated with Wilson. And the Texans postmortem wasn’t an isolated incident. Doug Pederson fired Wilson for various reasons but Cox’s viewpoint was given ample weight, sources close to the situation said.

Wilson, who is currently the defensive coordinator for the University of Colorado, didn’t respond to a recent interview request.

Cox might not even realize sometimes the pull he may have. One coach had Roseman approach him following a game with the request that Cox and defensive end Brandon Graham not be kept off the field at the same time. At the following practice, the coach relayed the information to Graham, and Cox, who overheard the conversation, confirmed that he had recently broached the idea, but not as a demand.

But his voice on the coaches continued to be heard. Phillip Daniels, who was Wilson’s assistant, was promoted before the 2019 season. A former player, he was popular in the D-line room, partly because he didn’t have favorites, two players said.

Daniels had played 14 seasons in the NFL and pushed Cox to maximize his abilities, whether it was in the weight room or the practice field, so that he could maintain his level as he aged. Offseason toe surgery slowed Cox’s return and a rash of injuries in the interior also contributed to the unit’s struggles.

The Eagles still finished 12th in sacks per pass attempt, but when the season ended there were rumblings in the NovaCare Complex that Daniels could be let go. Defensive coordinator Jim Schwartz wanted to promote longtime aide Matt Burke, but Cox was also a force in there being a change, team sources said.

Daniels survived the initial bloodletting, when offensive coordinator Mike Groh and receivers coach Carson Walch were axed, but Pederson fired him three weeks later, long after initial evaluations were made.

Daniels, who isn’t currently employed by an NFL team, declined to comment.

Eagles staffers, past and present, have split opinion on Cox’s elevated standing in the organization. It’s the chicken-or-egg argument: Is he the one pulling the strings or he is just taking advantage of what’s been given?

When Schwartz went to Roseman to tell him of his plans for Burke, the GM said something to the effect of, “Let me run it by Cox first,” a source familiar with the conversation said. Roseman may have similar conversations with other leaders on coaching changes. But after Cox’s role in the Wilson and Daniels firings, the GM’s response here spoke to his instincts.

Cox has gotten along with his share of coaches, starting with his first two position assistants, Jim Washburn and Jerry Azzinaro. He had few objections to Burke, who left this offseason like most assistants under Pederson. He has a close relationship with Jeremiah Washburn, Jim’s son, a senior defensive assistant who worked primarily with the line and was retained.

Washburn wasn’t tabbed as Burke’s replacement, though. New coach Nick Sirianni hired Tracy Rocker, who has nearly 30 years of coaching experience but only three of it previously in the NFL. He has the reputation of a taskmaster.

“Every D-line coach I’ve had coaches hard,” Cox said recently when asked about Rocker. “From Jim Washburn to Coach Azz to Chris Wilson to Phillip Daniels to Matt Burke. Every D-line coaches hard and that’s what D-linemen like.”

Cox didn’t practice most Wednesdays last season, a routine that started before he popped up on the injury report. Pederson had been known to give certain veterans rest days, but Cox was the most absent last season.

“I just do what I’m told around here,” Cox said last November when asked about the missed practices.

Cox has always been a freak of nature. His 4.79-second 40-yard dash at the combine has been topped by only two other interior linemen since 2012: Donald (4.68) and Milton Williams (4.67), the Eagles’ third-round draft pick in April.

The team has tried for years to find an inside complement to Cox. There have been some serviceable tackles, but never a comparable force who could draw consistent attention away from the 6-foot-4, 310-pound Cox.

Free agent Javon Hargrave struggled to adapt to a new scheme last season, but will likely be given a starter’s crack this season. Williams is viewed by many scouts as a raw prospect, but with Donald-like athleticism.

He’s a long way from translating that athleticism to the field, but the Eagles have a potential replacement at the three-technique spot should they part with Cox sometime in the foreseeable future. It’s more likely they restructure and extend his contract next offseason, though, as to account for natural waning.

It would be foolish to count out a return to form, as well. Cox’s play had slipped, but only marginally. And it’s unclear how much the various dings affected his production or hindered his conditioning. Despite the injuries, he’s only missed four games over nine seasons.

But there are still Eagles staffers who would like to see him dominate for longer stretches than just one or two games. Cox was arguably the best player on the field in the playoff loss to the Seahawks two seasons ago, but those moments haven’t come as often of late.

Perhaps it will take a new coaching staff to get him to again reach those heights. New defensive coordinator Jonathan Gannon’s scheme will keep a 4-3 base front, and presumably Cox in the three-technique role. But the term team defense has already been mentioned enough to make one wonder how much freedom the defensive tackle will be given.

“They basically said the same thing [as always], just be disruptive,” Cox said when asked about the new system. “Coach just wants me to be disruptive and play what style of defense I’m used to playing.”

Change is inevitable, but if Cox can turn back the clock, he can slow the rapid march into his 30s — at least that perception.