Without knowing the history and how well and often the previous owner used them, I would replace the front two and then have the rear four inspected and use one of the fronts if any fail the inspection. I would carry the best of the two as an unmounted spare on the roof. I went seven years on my front tires that I put almost all of the miles on and 10 years on the six rear tires. I did swap the two tag tires to the front at five years. All 8 tires are now on the back of my 10 wheel dump truck...14 years old.
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