Ive shot ammo fairly recently from WW2. Ive shot ammo, that still as accurate & reliable much older than that even.
Factory ammo over 30 years old properly stored [ in ammo cans, in a safe, in a bedroom] will outlast you.
Reloads? Well, anyone who knows me knows I dont shoot them, so their lifespan I cant comment on.
Im sure certain types of ammo can "go bad" if not given even semi -good care...but Ive shot enough old stuff to know age itself aint a factor.