Probably as soon as a tire company admitted there could be a problem,
the other companies would use it as a chance to act superior and gain
those tire sales. I imagine it is a stand-off.
I don't think it is the tire age factor, alone, but what usually happens
as tires age. Low operating pressures have the sidewalls flexing a lot,
which can heat the tires, and harden or break the reinforcing fibers.
On steel belted tires that is a real problem. Ask the Ford SUV's.
As the rubber sidewalls age, more quickly in sun or under inflation, they
crack. The cracks open more as you inflate the tires. Air and moisture
gets in there and can weaken the belts... especially steel belts. My
local tire shop has shown me some of these with Rusted broken belts !
The make of tire doesn't eliminate these problems.
I've had expensive tires separate more than cheap tires.
If I had perfect conditions, I wouldn't be worried about the age of the tire,
but of course, no one has perfect conditions.
Tom S
southern Ohio