I like reading these Age Profile charts. However it isn't as simple as just looking at where the bulk of the players lie. Goalkeepers and CBs can go on for much longer, 30-32 is prime for them. And there is the fitness improvement of modern players to consider, over their peers of yesteryear.
I don't see our group of players as being particularly 'old' yet. A gradual integration of 2-3 player transfers per Summer (see : Jota, Tsimikas, Elliott, Morton, Kelleher & Jones coming through) would see the squad rejuvenated.