A person of any age -- even one under 50 -- can join AARP as an "Associate" member for, I think, $16/year by calling AARP. You can check the AARP rates with Avis/Budget first to decide whether it makes sense to pay the $16. (Avis AWD A359800; Budget BCD Y508501. But don't book a car with those codes unless you actually join AARP; if you have an accident and can't show proof of membership, I would not expect Avis/Budget to honor any of the insurance benefits. And some locations will ask to see your AARP membership card at pick up.)