Modern Tires

From the NHTSA website:

• As tires age, they are more prone to failure. Some vehicle and tire manufacturers recommend replacing tires that are six to 10 years old, regardless of treadwear. You can determine how old your tire is by looking on the sidewall for your DOT Tire Identification Number (TIN) . The last four digits of the TIN indicate the week and year the tire was made. If the TIN reads 0308 it was made in the third week of 2008. Look on both sides of the tire. The TIN may not be on both sides.

I should add that the four digit DOT date code started somewhere around the year 2000. Older tires may have a three digit code where the third digit is the year. Whatever the case, don't risk damaging a nice fender or quarter panel just because you don't believe the hype. There is a reason a bunch of campers and trailers are always on the side the of the road with a blown tire, and it is not always inflation to blame.