I know this is an old thread, but the dates are stamped on the tires.
1. Look on the tire sidewall for a string of letters and number that start with "DOT." The string is over 10 digits long. If you find just "DOT" followed by less than 10 letters and numbers, then the full DOT number that you need is located on the other side of the tire.
2. Go to the end of the DOT number and write down the last four digits. They should all be numbers, like 3199 or 1506. These numbers indicate the date of manufacture of the tire.
3. Decode the tire date. The first two numbers are the week of the year, and the last two numbers are the year of manufacture. For example, "3199" means the tire was manufactured in the 31st week of 1999.