Tons of interesting stuff here...
It's well known that most players peak between age 27 and age 29, and the data backs that up. Note that BA, OBP, and SLG are all higher for players between 26 and 30 than for any other group.
On a per-plate-appearance basis, the Age 26-30 group also leads in doubles, homers, stolen bases (and CS), and walk. Players 25 and under lead in triples and strikeouts.
Notice how BAbip drops as players get older--I'm guessing that's an effect of fewer infield hits as players slow down a bit with age.
Game starts--44.3% of them were made by that Age 26-30 group. The youngsters started 24.2% while the 31-35 year olds started 25.6%. The oldest group started just 5.9% of the games.
Oh my how things have changed. At the height of the Steroids Era in 2001, look at the same breakdown:
Suddenly there's much less of a gap between that leading group (Age 26-30) and all the older players. In fact, The oldest group has nearly the same OPS as the 26-30 guys. It's the really young guys who performed well below other folks.
And check out how the game starts break out.
Only 42.6% were started by the Age 26-30 group (as compared to 44.3% in 2011). The youngsters started 22.1%, the 31-35 year olds started 27.4% and the 36+ group started 7.9%.
In 2001, players 31 and older started 35.3% of the games, but in 2011 that number was down to 31.5%. You probably won't find any better statistical proof that use of banned substances extended careers.