I recently retired a 95 Intrepid that started as my wife'* car and was over the years passed down to my son, and then to my daughter. My nephew has an 01 Intrepid, so we scavenged some parts off our car for him. We realized the full size spare tire had never been used, and looked like new. After some research we decided to scrap the tire.
Take a look at this:
The scary thing is there are some unscrupulous tire places that are selling tires as new, that have a shelf life well over 6 years.
This article explains how to decode the numbers on the back of the tire to determine what the manufacture date was:
Kinda makes you want to go check the back of your tires, doesn't it?
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)