If tires are stored inside, they will keep for years and years. There is a limit, but they are not like fresh produce. I have a stash of tires and tubes that will take several years to use up. It might be more of an issue for racing tires where you want them soft and grippy, but I doubt if you or I could tell if a tire is 3 months old or 3 years old. They sit on bikes in garages for years all over America without falling apart.