Use an Avis AWD or Hertz CDP that has the underage waiver included. A lot of corporate ones allow underage drivers to drive the nicer vehicles as well.
Just ensure that you actually qualify for the AWD/CDP, especially if you're underage. Ask your company if they have one or see if any of your frequent flyer/insurance/credit card etc. have this included. I never had a problem renting the nicer stuff when i was younger.