From an ebay seller...
If I made a huge mistake like that in a listing, then I would have immediately offered a refund. I would not care about what was legal or not. I would care about doing the right thing. You seem to be trying to get away with as much as you can. Why? Just pay for the tires and resell it. And now you will be able to say the tires are brand new. Maybe you'll recoup the money for the tires, or even more than what you paid for them.
Whether it was intentional or not, you made the mistake and misled the buyer. Don't you at least feel a little bit bad for HER? How would you feel if the tables were turned and you bought a vehicle that was 5 years older than what you were told?