Believe it or not, male sprinters can, and often do, peak around 30 yrs of age.
Without getting too deeply into it, check out some of these guys:
Lewis 9.86 @ 30
Bailey 9.84 @ 29
Surin 9.84 @ 30
Gay 9.69 @ 27 and not yet done
Gatlin 9.80 @ 30
Fredericks 9.86 @ 29
etc.
I actually believe, somewhat, that PR'ing substantially earlier, in early/mid-20's, might be some evidence of doping, unless they are constantly injured in their late 20's/early 30's. Guys get much stronger in their late 20's/early 30's, and by that time have learned how to train better, and have had time to let their training take hold. Also, they're not as freaked-out at meets, and become more accustomed to travel.
The athletes I listed, and their times, would seem to lend some credence to the idea that 'roids allow you to achieve your potential sooner than you would naturally. This is not inconsistent with the idea that 'roids make you better than you could ever be naturally--both effects could certainly manifest--you're better than you ever could be naturally, and sooner as well.
Gatlin running 9.80 at 30 is absolutely not anomalous, and by itself is not good evidence of current PED use. The question of whether he is currently enjoying lasting benefits from prior PED use remains unresolved.