My Dad has some 22LR ammo that's been sitting for 25-30 years in a dresser drawer. Does ammo have a shelf life? He also has some 20 gage shotgun shells that have been sitting about the same amount of time.
Most of mine (12ga, 308, 9mm, .45) is from the 90's, during Clinton's assault on the 2nd. Never had a problem. Got a bunch of 7.62x54 from the 1950's, a couple of non-fires out of several hundred shots. "Keep your powder dry".
The biggest enemy of ammo is high heat storage, or excessive vibration (that breaks up the powder kernels and makes them burn faster=high pressure). I'd be more worried if the ammo had been in the pickup truck's glove box for 20 years, for example.
I shot up some stuff my grandfather bought in the 1950's ( remington ) , stuff was heavily wax coated , actually shot better than some new Winchester white bulk stuff, it was kept in a gun cabinet for all them years only 2 FTF's and that was because the wax prevented the striker from hitting .