Compared to days of old, tires, especially "performance" tires, are made of rubber compounds that get REALLY hard with time, starting at about 5 years, but by 10 years old, they are hard as polyurethane skate board wheels.
I've got a pair of PS4Ss that literally have gained 20 points on the durometer scale.
They still "function" for basic city driving, but they have lost most of their grip.
Very sad because they have most of their tread depth, but are useless for the track and absolutely have to be replaced before my next track day.
This is why some tire shops wont touch tires older than 10years, they claim they can be dangerous to handle due to the rubber compound being "hard".