That's not a stupid question at all. I had the similar experience trying to avoid the underage charge. I did some research on that matter and what I found was, enterprise was the most lenient and friendly car rental company in my area. (among Budget, Avis, National, Hertz). I went to enterprise office and asked if there is anyway i could avoid the underage fee. At first, the attendant told me I have to pay it but finally he agreed not to charge the extra fee when i rented the car for a week. It depends on you how you approach and talk to the representative of the particular rental company. Do not make the mistake of taking about that issue over the phone, they will just deny it.