you can usually tell if the belt has been changed because the engine mount on the right, when looking at the engine, will still have paint on the bolts. I've snaped a belt on my crx at 120 miles. changed the belt twiceon my 92 integra at 100k and it still looked good. my friend snaped a belt on a 95 civic at 150k miles.

no bent valves in any of these incidents.
Never heard of the age thing. I say i would go by how many miles the car has.

you guys are making me paranoid now, cuz im about to buy a used 01 accord has 40k miles but the last owner barely drove it. i'm wondering if i should change it at 80k..

I say if the car has been used regularly, your safe till 100k.. But if you like to drive hard change it out sooner. like 80k.