I remember opening cans of 9mm Ball Ammo on our pistol shoots in the military which was stamped 1955 and it worked awesome in the Browning Hi-Power and Sig's. The ammo looked like it was manufactured yesterday, still nice and shiny.
I've also purchased 7.62mm surplus from a local dealer here for use in my .308, it was dated 1967 and worked awesome aside from being pretty hot as well.
Goes to show you that if its kept in a cool, dark and dry spot, you could easily keep it for decades.
Cheers,
Exercitus