Modern Tires

10 years is the current max life as far as I’m aware, that’s per most of the tire manufacturers. That’s the hard/fast time though, as in most tire shops won’t even touch them at that point. Apparently a lot of automakers are now recommending 6 years, because of the number of incidents with tires over 6 years old (liability, like RRR said). More info here How Old - and Dangerous - Are Your Tires? | Edmunds

And if they show any signs of degradation the tire shop may recommend they be replaced sooner. I know at the 6 year mark I’ve seen signs of checking and cracking on modern tires. Depends on a lot of things- UV exposure, the number of temperature cycles on the tire, general use, maintenance, etc.

As far as old tires lasting longer, maybe. But they also didn’t have anywhere near the grip and performance of more modern tires. Everything’s a trade off. You want tires that will pull .9+ G on the skid pad, work in the rain and maintain good grip over a wide temperature range then maybe they won’t last as long, but that’s far better performance than older tires ever gave. Modern tires absolutely “time out”. But you wouldn’t catch me running 40 year old bias ply’s on the freeway either, I don’t care how good they look.

Bottom line is, what’s it worth to you? That old tire lets loose and takes out your fender or quarter panel it’s gonna set you back a lot more than a set of tires. And that’s if it doesn’t put you into a telephone pole or a K-rail. If you're bent out of shape because your tires are aging out before they wear out maybe it’s time to drive more?