I've heard everything from 6 - 10 years for a "best before" date. I think 6 years is a conservative estimate, but either way, if they're 8 years old now, you've got to factor in that you might have to replace them in 2 years. $350 for two seasons, with the potential they might last longer, doesn't seem too bad. I would definitely want a visual inspection of the tires first, and if they'll do it, see them mounted and installed on the car.