I forgot to mention a delightful experience I had while on vacation.
Leaving LAX, we hopped on a courtesy shuttle from Hertz that took us to the offsite rental office. When we arrived, I was politely told I had to be over 25 to make a reservation; a little disappointing, but fairly typical. On the off-chance, I asked whether they had any suggestions for places that might not have the restriction. 'Certainly, just go over there and ask that lady'.
We headed over and I rather sheepishly described the situation. 'Sure we can help' - she called up another company and handed me the phone to make the reservation. Before I handed it back to her, she'd already arranged for a guy to run us over there in a courtesy shuttle. As I thanked her, she smiled and in a perfect display of company line simply said 'No problems - only solutions'.
It has to be said, service in America is generally top notch. Hertz have done a great job in gaining my loyalty; I'll certainly rent from them in the future, when I'm old enough.