All tires are required by law to have a manufactured date code molded into them. Look near the DOT letters, you will find a multi-digit number. The last four digits are the date code. If the number were 5104 it would mean the the tire was made in the 51st week (December) of 2004. Prior to 2000 this was a three digit code with the first two being the week of manufacture and the last digit the year.
Hope this is what you were looking for.