This has been covered before, but it's always worth a reminder.
"Properly stored tires that are protected from the elements and not mounted on a wheel age very slowly before they are mounted and put into service.
Our experience has been that when properly stored and cared for,
most street tires have a useful life in service of between six to ten years. And while part of that time is spent as the tire travels from the manufacturing plant to the manufacturer's distribution center, to the retailer and to you, the remainder is the time it spends on your vehicle."
http://www.tirerack.com/tires/tirete...jsp?techid=138
The tires on most of our cars will age out long before they wear out.