when Should I change my OEM Potenza tires?

[Loren]

I'm going to side with your friend, sort of. Tires do harden and deteriorate with age, regardless of mileage and remaining tread depth. After 2 years in the elements, they will be noticeably less soft and less grippy than they were when new. That said, it's not uncommon for people to run a set of tires for 5 years or more... so it's really up to you how long you're willing to leave a set of tires on your car.

Personally, my tires never last 2 years. I do a lot of autocrossing and occasional track driving in my car, and I think my record is about 11 months.

But, on my wife's car, I regularly insist that she replace her tires about every 3 years... usually at about half tread depth.