Old ammo is fine to shoot with the exception of military ammo with corrosive priming prior to the 1950s or so.

I've mentioned this before: My 94 year old father passed away two years ago. I was cleaning out his Jeep Cherokee and in one of the rear cargo compartments, I found a leather belt strip holding about a dozen .30-06 cartridges, I rig I gave him and had forgotten about. He hadn't hunted in more than 15 years.

Despite 15 years of alternately baking and freezing through New York winters and summers, I removed the accumulated verdigris from the ammo and it all fired like it had been made yesterday.