Two words of warning here.

1) My wife was under 25, and the only way we could rent a car that both of us could drive was for her to rent it, and I would be the additional driver. We had to pay an under aged fee and have a credit card in her name. This worked OK until we turned up at a Budget rental desk in a minor airport. They refused to rent us a car because of my wife’s age, saying that they did’nt rent to under 25s, even though the reservation was made by phone and had additional info regarding the age int he comments on the reservation. I said ‘ yes you do, and it even says you do in the Budget policy document on the internet’. The manager countered by say that they were a franchise, and could make up there own rules !
2) Watch out on the insurance front. I’m not sure if it’s the same in the US, but if you’re unfortunate and have an accident, you might find your insurance invalid even though they took your money at the time of rental if you aren’t infact entitled to the insurance. I think this is called underwritten at the time of claim. ‘Normal’ car insurance is underwritten at the time of policy issue, and is valid unless you break the insurance rules.