Perhaps it is time for me to step in and comment on the subject of tire age.
First problem: Tire aging is highly dependent on temperature. Tires in - say - Phoenix - age much faster than tires in - say - Minneapolis. How does a government set a regulation with such a spread of conditions?
Second problem: The US Federal government can only set regulations for interstate commerce. That means they can only regulate trucks, airplanes, etc,, not passenger cars.
Third problem: The US Federal government can only regulate things where there is an issue. Is tire age such a large problem that the feds need to step in?
Fourth problem: What data do you base a regulation on? Where do you draw the line? Tire failures due to age isn't a bright line kind of thing!
What that means is the states are where passenger car tire regulations have to come from and there isn't clear data to set a regulation.
Clearly there is an upper limit, but what is it?
Here's what the USTMA (US Tire Manufacturers Association) says about it:
"USTMA is not aware of scientific or technical data that establishes or identifies a specific minimum or maximum service life for passenger and light truck tires. However, in some cases a tire or vehicle manufacturer may make a specific tire replacement recommendation regarding its products. If so, the consumer should consult the manufacturer with any questions with regard to following the recommendation. Furthermore, any such recommendation should not be considered a minimum service life for the tire.”
For more detail:
Barry's Tire Tech: Tire Aging and Weather Cracking