The average age of the Patriots' current roster is 25 years old. (NFL Game Rewind)

The average age of the Patriots’ current roster is 25 years old. (NFL Game Rewind)

It’s hard to say when it started, but it’s clearer now. A youth movement is underway inside Gillette Stadium.

This March saw the 33-year-old Vince Wilfork, the 30-year-old Brandon Browner and the 29-year-old Darrelle Revis leave the defensive side of the ball. And it saw the 32-year-old Dan Connolly remain unsigned along the offensive side, after the team’s third-longest tenured player, the 33-year-old Logan Mankins, was traded last August.

Yet it isn’t so much about whom will replace them. It’s how.

There have been 13 free-agent additions in preparation the 2015 NFL season. Only one, a reserve-future signing and ex-Tennessee Titans defensive lineman named Antonio Johnson, has already hit his third decade. There have been eight free agents retained. And only two, kicker Stephen Gostkowski and defensive tackle Alan Branch, have reached that same point.

In result, the average age of a New England Patriots player – at the moment – is 25 years old.

It is hard getting older. And, in a sense, the same can be said of getting younger. New England’s 75-man roster is heading that way in football years, as head coach Bill Belichick and director of player personnel Nick Caserio have gradually shed spare parts and key pieces of the Super Bowl XLIX team, which was already the youngest of its kind in NFL history.

But that business approach has always been the goal. It is not new, trying to find a balance between the two, incorporating the talented, affordable and unproven with the skilled and seasoned in aim of longevity.

And in a month, the former will deepen along with the rights to nine draft selections and a pool of undrafted free agents as the roster fills to 90 players.

It is a process – drafting, signing, re-signing, trading and releasing. Within it, there is constant turnover. That is illustrated in the fact that only one player is left from New England’s Super Bowl XXXIX team that defeated the Philadelphia Eagles in February of 2005.

He will be 38 in August. He is quarterback Tom Brady. And he is one of only six Patriots currently beyond his 30th birthday.

  • Age 37: Tom Brady
  • Age 31: Rob Ninkovich, Stephen Gostkowski
  • Age 30: Sebastian Vollmer, Alan Branch, Antonio Johnson

There are pillars there in the over-30 club in addition to No. 12. It is, however, an exclusive group for a reason.

Gostkowski became the Patriots’ all-time scoring leader this past season and set a franchise conversion mark at 94.6 percent, prior to being tagged before the new league year began. Defensive end Rob Ninkovich is also in that tier, after recording 1,000 snaps for a fourth consecutive season and eight sacks for a third, earning a pay raise this past month. And right tackle Sebastian Vollmer, a 67-game starter who’s battled through injury to remain one the better bookends in the league, is among them as well.

The likes of wideout Danny Amendola, former Bills tight end Scott Chandler, green-dot linebacker Jerod Mayo, and Pro Bowl special-teams captain Matthew Slater will join them as the Patriots head into the upcoming season. All four also have their merits on the elder side of the ledger.

  • Age 29: Danny Amendola, Scott Chandler, Jerod Mayo, Matthew Slater

Yet the rest of New England’s roster – a total of 66 players and 24 of the organization’s draft picks – is 28 and under.

That list is a long one, and it features a three-time All-Pro tight end, a 1,000 yard receiver, a newly re-signed defensive captain, two 25-year-old starting pass-rushers and a pair of linebackers who finished 2014 graded among the NFL’s best.

  • Age 28: LeGarrette Blount, Julian Edelman, Brandon LaFell, Kyle Arrington, Bradley Fletcher
  • Age 27: Brandon Gibson, Jordan Devey, Patrick Chung, Devin McCourty
  • Age 26: Travaris Cadet, James Develin, Brian Tyms, Michael Hoomanawanui, Nate Solder, Marcus Cannon, Joe Vellano, Jake Bequette, Chris White, Chimdi Chekwa, Robert McClain, Nate Ebner
  • Age 25: Brandon Bolden, Kevin Dorsey, Rob Gronkowski, Josh Kline, Chandler Jones, Jabaal Sheard, Dont’a Hightower, Jamie Collins, Jonathan Freeny, Darius Fleming, Alfonzo Dennard, Malcolm Butler, Tavon Wilson, Ryan Allen
  • Age 24: Jonas Gray, Dion Lewis, Tim Wright, Bryan Stork, Chris Barker, Sealver Siliga, Chris Jones, Michael Buchanan, Zach Moore, Rufus Johnson, Deontae Skinner, Daxton Swanson, Justin Green, Logan Ryan, Duron Harmon
  • Age 23: Jimmy Garoppolo, Garrett Gilbert, Tyler Gaffney, James White, Aaron Dobson, Josh Boyce, Jonathan Krause, Caylin Hauptmann, Dominique Easley, Eric Martin, James Morris, Cameron Gordon, Tyler Ott
  • Age 22: Cameron Fleming

New England presently carries 58 players age 27 or under. There are 54 age 26 or under, 42 age 25 or under, 29 age 24 or under, and 14 age 23 or under.

The volume in those numbers will inevitably reduce in time, as the 75-man roster branches out to 90 only to be pared down to 53 by September. All the while, the age in those numbers will inevitably grow older. That is the way it is, and the way it has been. Yet this year, perhaps there’s more than the age of the Patriots’ roster that’s striking.

With New England still slated to return all but four of the offensive and defensive starters from the 2014 team, and with Connolly still a candidate to cut that number to three, perhaps it’s the way it stands up against time.

The headlining free-agent departures may signify a new era for the Patriots. But on paper, it’s very much a continuance of the same one.