Looking at ages of players on teams, hardly tells you how old the team is.
Project out the average age per minute played to get a better feel.
If you expect KG & Bass to play 30, Ray & Pierce to play 32, and Rondo to play 40, then your starting lineup is averaging 30.9 per minute. An in basketball terms, that's old.
Even if everyone had been healthy - AB (third guard - 24 MPG), Jeff Green (sf/pf - 24 MPG), some combination of steisma, JO, and Wilcox getting rest of big minutes, the average minute player would still be ~29.5.
You get different answers, and I'm sure there are problems with methodology, but basically players peak in their mid to late 20s. See this
for example. Now - I'd still rather have old elite talents especially tall players, that play well together, and can shoot - but breaking up the big 4 so one of them is on the bench at the start of the game, seems to make a lot of sense.
My thought is that should Pierce, so he can play every minute when Rondo sits. As the two of them are the best creators on offense - and so he doesn't have to take the workload he does defensively - best wing players in the NBA are at SF, not SG, IMO.