Tire age

My tire guy says that he is informed that the tires dry rot from the inside out. There is air on the inside and that causes the dry rot. Nothing you can do to stop the inside dry rot regardless of being aired up or on blocks or out of the sun.
After 7 years the manufacturer says to replace all tires.
I always figure that's a ploy to get us to buy more stuff.
Regardless, we see tires go bad and they are usually older than the 7 years.