Funny, you should say that about having to be 25 to rent a car. Back a few years when I was building time and doing cross countries I took my girlfriend to BHB Bar Harbor ME for the day and I wanted to rent a car. I had credit card and everything but insurance required me to be twenty five to rent a car. I just thought it was so crazy because when I was student pilot I could rent a little warrior fly my solo X/C's all over the place and I was just 16yrs old at the time. It seems ridiculous that you can rent a plane by yourself at 16 but, you need to be twentyfive to rent a car. Even more nuts you could if you get hired young enough you could potentially be captain at 23 or 24yrs old and still not be old enough to rent a car. So in the end the FBO just gave us a courtsey car which really doesn't seem much different than a rent a car but oh well. Just my .02 cents