One of the oddities was that I was old enough to rent a plane, but not old enough to rent a car. ???
Think back on how you learned to do both, and the reason should become clear.
Odds are, you were taught to drive by a parent who had been taught by their parents. Then you were examined by a guy who basically made sure you stopped at lights and signaled before turning; the hardest part of that test probably was parallel parking.
And then you had a license that entitled you to drive in city traffic or over icy mountain passes, by day or night. Maybe you were good at it then, maybe not; the point is, nobody knew the answer to that,
especially the insurance industry. So you had to
show how good you were, by getting to age 25 without killing anybody, before Hertz's insurance company would touch you.