ORCHARD PARK, N.Y. -- After the Buffalo Bills replaced their entire coaching staff and front office this offseason and traded away one of their top players, Sammy Watkins, this August, it is fair to say the team is the midst of at least some degree of a rebuild.

However, the Bills' opening-day 53-man roster was the second-oldest in the NFL, averaging 26.81 years old, according to data released Thursday by the league. Only the Arizona Cardinals, averaging 27.47, had an older roster to begin the season.

How does Buffalo reconcile the relatively advanced age of their roster with its philosophy of building a contender in the long term? Coach Sean McDermott reiterated Thursday his belief that his team needs veteran leadership to shape its younger players into leaders of the future.

"Hopefully with [the age] comes wisdom," he said. "In my experience, I've been around some older teams, and they were pretty good teams. Really, it's trying to win now and sustain in the future with putting a good foundation.

"The good part about is you have the older guys that can show the younger guys the way. Then we've got all of our draft picks that are watching these older guys lead. They're the second crust of leader guys developing, watching these older guys here. So that's a good blend."

The "second crust" of young players the Bills have to develop consists mainly of their 2017 rookie class. The Bills had 12 rookie and first-year players on its opening-day roster, tied for the eighth-most in the NFL.

Buffalo also had 10 players who were 30 years or older, the fifth-most in the NFL. That means the middle class of the Bills' roster, at least in terms of age, is thin. That is partly the product of McDermott and first-year general manager Brandon Beane parting ways with nine of former GM Doug Whaley's draft picks from the 2014 through 2016 classes.

The Bills figure to trend younger in the coming years. They have eight draft selections in 2018, including six in the first three rounds. Added to the 2017 draft class that the Bills' current management group is more likely to retain than previous draft classes, the Bills have the opportunity to build a young core.

Older players could also depart next offseason. Of the 10 players who were 30 or older to start this season, only four are under contract next season: guard Richie Incognito, center Eric Wood, linebacker Lorenzo Alexander and kicker Stephen Hauschka.

Meanwhile, defensive tackle Kyle Williams, running back Mike Tolbert, safety Colt Anderson, quarterback Joe Webb, linebacker Ramon Humber and cornerback Shareece Wright are all scheduled for free agency.