It really depends on the way you store them. Case in point - about 10 years ago, I picked up a set of 195/75-14 Goodyears for a really good price. Was going to use them on an old Chevy I was driving at the time. Problem - the car gave up the ghost before I needed them. Put them in the attic of my Dad's barn. (This is in Florida). They stayed up there a cooked for a decade. When I needed a set of 14's recently, I remembered those tires up in the attic. Took them down and they were as hard as rocks. When ahead and put one on my van. Blew out in less than a mile.
Conversely, when I was in college, (20 years ago), I picked up a set of mudders for my truck. Put them downstairs in Dad's barn, in a dark, cool place. Just put them on my truck last year, they are still running strong.
Where ever you store them, don't stack them one on top of the other. The tires on the bottom will fold together from the weight of the tires on top.