I noted that my dad's 2008 Civic manual stated that under no circumstances should you run tires more than 10 years old. I think this was about the time a few rollover crashes were attributed to old Firestones, and tire manufacturers (yes, who have an interest in selling more tires and not getting sued) were recommending new tires every 5-7 years regardless of tread depth.

I'm sure there are plenty of people driving around on ancient tires and are still alive. But I feel that rubber products all seem to rot away no matter how nice their environment, and car tires can take a beating. Being a belt & suspenders type of person, I would like the reassurance of "safe" car tires, so I've been changing tires about 7-8 years, even if they otherwise look OK and they have plenty of tread. The new tires always seem to grip and perform better anyway. 25 y.o. car, averaging 4k miles year.