I have a fifth wheel with Goodyear G614 G rated tires. They still have very good tread and still look good but they were made in the 19th week of 2014. I read that you can go between 6 to ten years....
I'm going to try to get 8 years out of my last almost 7 year old Michelin XPS Rib. (Michelin states replace after 10 years regardless of mileage) I lost one with a Wheel (!), and one to a Nail. I'll let you know if this summer's travels prove me wrong....