What law is that? Only a few states have laws regarding the age of tires being sold new and there isn’t a Federal one. The state laws are small fines only.
There is actually such a law. It doesn't ban the sale of tires that age however it states that tires older than 6 years old are not to be sold as new tires and must be sold as used tires.
According to the DOT Federal Motor Vehicle Safety Standards; Tires, 68 Fed. Reg. 38,116 (June 26, 2003) (to be codified at 49 C.F.R. pt. 571). Cited by Ammons Law Firm, May 2014