Look at the date code on the tires. What matters MORE than age is how they have been maintained and stored. If stored inside all the time, you can actually get good and safe use from 15-year-old radials. If not stored inside, the Sun and ozone damage are the things that destroy a tire. I'd offer the seller a price as if the tires were NOT part of the deal - you are going to trade the tires off when you get new ones, anyway, for the $2.00 disposal fee each.