We were trying to figure out how old our tires were the other night. Here's how we can tell. I got this from the Michelin website
How do I know how old my tires are?
Each tire has a required Department of Transportation number imprinted on at least one of its sidewalls. That number begins with the letters "DOT" and may contain up to 12 additional numbers and letters.
The first and last digits are the most important for the tire owner. The first 2 letters/numbers identify the manufacturer of the tires. Prior to the year 2000, the last 3 digits of a DOT number represented the week (2 digits) and the year (1 digit) of production.
For example, if the last three digits are 439, the tire was produced in the 43rd week of 1999. Tires produced after January 1, 2000 have a 4-digit date code at the end of the DOT number. The first 2 digits represent the week of production and the last 2 digits represent the last 2 digits of the year of production. So, 3500 as the last 4 numbers indicates that the tire was produced in the 35th week of the year 2000.
Hope this helps