Brain maturation (fronto-cortical pruning) is not complete until 26 years of age.
Ever notice how you can work at 16, vote and be drafted/enlist at 18, drink at 21 but can't rent a car without a co-signer until 26?
Now you know why. Car rental agencies don't study human neurophysiology, but they damn well know there's a difference between people who rent their cars before and after 26.
It's almost as if Florida has somehow offended God.