Measuring team age in the N.F.L. is tricky. Calculating the average age of a 53-man roster is misleading because the age of a team’s starters is much more relevant than the age of a team’s reserves. The average age of a team’s starting lineup isn’t perfect, either. The age of the quarterback and key offensive and defensive players should count for more than the age of a less relevant starter. Ideally, you would want to calculate a team’s average age by placing greater weight on the team’s most relevant players.

That’s not easy to do for the 2012 season, but we can apply one method to last year’s rosters. Using Pro-Football-Reference’s Approximate Value system, it’s simple to calculate the weighted age of every team last season, by weighing each player’s age proportionately to his percentage of contribution (as measured by the Approximate Value system) to his team.

Let’s take a look at the (weighted) average age of each offense last season:

Offense

It’s not too surprising to see Seattle at the youngest team in the league last year, and they look to have a young offense again in 2012. The Seahawks will get younger at quarterback if either Matt Flynn or Russell Wilson replaces Tarvaris Jackson. At wide receiver, Sidney Rice (26 in 2012), Doug Baldwin (24) and Golden Tate (24) are the projected top three, although the team just added 29-year-old Braylon Edwards. Marshawn Lynch is still just 26, and the Seahawks added Utah State’s Robert Turbin in April’s draft. The offense line, anchored around LT Russell Okung (25) and C Max Unger (26), has all five starters under the age of 30, as are both Zach Miller and Kellen Winslow, Jr..

The Patriots, meanwhile, featured the league’s oldest offense last season. We all know about Tom Brady (34 in 2011) and Wes Welker (30), but Brian Waters (35), Matt Light (34), Logan Mankins (29), and Deion Branch (32) made were older members of the Patriots’ supporting cast. New England has a pair of young tight ends (Rob Gronkowski, Aaron Hernandez) and young running backs (Stevan Ridley, Shane Vereen), but the rest of the offense remains old. Obviously Brady and Welker continue to play at a high level, but the team didn’t wasn’t focused on age when it added wide receiver Brandon Lloyd (32).

The names are different on the line in New England, although not necessarily younger. None of the five starters in Super Bowl XLVI worked in the same spot at the start of training camp. Light retired and Waters is debating whether or not he will follow suit. Mankins, now 30, is recovering from ACL surgery, and it is unknown when he will return. Center Dan Koppen missed nearly the entire 2011 season with an ankle surgery; while he is returning to his old position in 2012, he turns 33 in September. Right tackle Sebastian Vollmer has joined Mankins on the PUP list, which meant Nate Solder, Robert Gallery and Marcus Cannon were getting reps for the Patriots. As long as Brady remains healthy, there’s not much to worry about, but New England will be relying on an old set of wide receivers and several offensive linemen dealing with injuries, age issues, or both. With any other team, it’d be worth considering that the offense is going to be relying significantly on older players. But it was just two years ago that I expressed the exact same concern about the New England offense, and it certainly hasn’t slowed down since then.

Defense

I wrote about the great job Wade Phillips did for the Texans last season, and he turned around Houston with one of the youngest defensive rosters in the league. Phillips’ group is well positioned to be strong defensively for the foreseeable future, even without Mario Williams. The team has young stars at every level of the defense: DE J.J. Watt (22 in 2011), ILB Brian Cushing (24) and CB Johnathan Joseph (27). Along with Brooks Reed (24), Connor Barwin (25), and Brice McCain (25), Houston’s defense was young and talented in 2011. With the addition of Illinois’ Whitney Mercilus and Nebraska’s Jared Crick, the Texans defense continues to add quality young talent.

After one week, Warren Sapp loudly declared that Pittsburgh’s defense was old and slow, and that it was over for the modern Steel Curtain. As it turned out, he was only right about one thing: Pittsburgh was very old last year. In 2009, 2010, and 2011, Pittsburgh’s starting linebackers were James Harrison and LaMarr Woodley on the outside, with James Farrior and Lawrence Timmons on the inside. Farrior retired in the off-season, but will be replaced by Larry Foote. Foote (32) and Harrison (34), are on the wrong side of 30, but the other two Pittsburgh linebackers are in the primes of their careers.

The bigger concern may be in the secondary. Cornerback Ike Taylor (32 in 2012) and safeties Troy Polamalu (31) and Ryan Clark (33) have seemingly been Steelers forever, and the secondary is never where you want to be old. On the defensive line, Brett Keisel turns 34 and Casey Hampton 35 this year, with the latter coming off knee surgery and currently on the physically-unable-to-perform list. There’s no getting around it: Pittsburgh’s defense was old last year, and will be old this year. Incredibly, six of the defensive starters on the 2006 team are projected starters for the 2012 Steelers. But Pittsburgh ranked 1st in both points and yards allowed last season, so even a small dropoff may not mean much. And let’s not forget, in addition to Timmons and Harrison, Pittsburgh has youth in the front seven with Cameron Heyward, Jason Worilds, and Evander Hood, and some young but untested players in the secondary.

Overall

Seeing St. Louis as the oldest team might surprise you. The Rams offense was basically meaningless when calculating their age because it was so ineffective last year; as a result, 67% of St. Louis’ team AV comes from their defense. And their only offensive player with any notable AV was 28-year-old Steven Jackson.

On defense, the secondary was decimated by injuries; Quintin Mikell was the only player with 16 starts, and he was 31. The front seven outside of James Laurinaitis and Chris Long, had an average age of 32 years, as James Hall (34), Justin Bannan (32), Fred Robbins (34) and Brady Poppinga (32) were all starters in 2011 for St. Louis. So with no standouts on offense besides Jackson and in the secondary besides Mikell, the front seven is responsible for much of the age-AV, and they were old.

Of course, AV is heavy on “approximate” and it should be taken with huge grains of salt when looking at just one team in one year. But according to age-weighted AV, the 2011 Rams were the oldest team in the league. Mike Sando highlighted the Rams turnover since the end of last season; when I told him my results, here is what he had to say. It certainly portrays the future of the Rams in a more positive light:

The Rams had one of the oldest teams in the NFL last season by average age. They subsequently got rid of many older players, bringing down the average. Last season is irrelevant, or close to it, when a team turns over the roster. The Rams were quite young in 2010, but they got older last season by filling their roster with a ton of vets to mask the absence of young depth on their roster. They justified it by noting that none of the older players they added was signed to a deal with cap implications beyond 2011.

Then, by late March, the Rams were becoming one of the NFL’s youngest teams again. This is how the changes were coming into view: http://espn.go.com/blog/nfcwest/post/_/id/62061/an-update-on-the-rams-youth-movement

The team did not re-sign its own UFAs. So, guys like Al Harris, A.J. Feeley, Tony Wragge, Brady Poppinga, Donnie Jones, Adam Goldberg, Jacob Bell, Brandon Lloyd, Rod Hood, Cadillac Williams, Gary Gibson, Mark Clayton, Stephen Spach, Mark LeVoir and James Butler — all 29 or older when free agency hit — came off the roster. The Rams filled most of those spots with younger players.

On the young side, Tampa Bay comes in as the youngest team, which shouldn’t surprise. Everyone knew that Raheem Morris was coaching a young roster, which didn’t turn out to be a good fit. Thanks to a ton of cap space, Tampa Bay signed Carl Nicks (from New Orleans), Vincent Jackson (San Diego), Dallas Clark (Indianapolis) and Eric Wright (Detroit) in the off-season. So who will be the youngest team in 2012?

Cleveland is an interesting candidate. Brandon Weeden is actually three years older than Colt McCoy, but the rest of the Cleveland offense will be very young in 2012. Obviously Trent Richardson was the key acquisition, but rookie Josh Gordon joins Greg Little (23 in 2012) and Mohamed Massaquoi (26) to give Cleveland a very inexperienced but young skill position players. Everyone knows Pro Bowl LT Joe Thomas (28) and C Alex Mack (27), but LG Jason Pinkston (25) and RG Shawn Lauvao (25) are even younger. Mitchell Schwartz, drafted with the 37th pick out of California, is the leading candidate to play right tackle for the Browns. Defensively, DT Phil Taylor (24 in 2012), DT Ahtyba Rubin (26), DE Jabaal Sheard (23), LB D’Qwell Jackson (29), and CB Joe Haden (23) form the core of an underrated Browns defense. If the Browns get good play out of Weeden, they have the pieces in place to be a playoff contender for the next several years.