Discount Tire just lost my business

I grew up around tires (my Dad owned a Goodyear Store for over 30yrs) and you would think I would know better. These had slite dryrot but the tread was still real good and I never thought about checking the serial date on the tires when I bought the car. If I did... I would have seen that the tires were over 15yrs old!
I was going over a bridge when this tread separated from the tire- thank God the tire did not blow and actually held air for about an hour after blowout.
See my thread (#46) http://www.forabodiesonly.com/mopar/showthread.php?t=82832&page=2
Old tires are not safe. Whats considered old? Ill let everyone decide for themselves...