I'm pretty sure I would have been fine driving a car as soon as I could reach the pedals, and school was a waste of time after 5th grade; why did they restrict

I'm pretty sure I would have been fine driving a car as soon as I could reach the pedals, and school was a waste of time after 5th grade; why did they restrict my freedom when in the latter case I'd at most harm myself? There were obvious and severe problems with that. Somehow we decided that after a certain age you can do whatever you want (more or less) and the constraints that arise from the fact that you are incapable, and dependent on care, stop applying. THAT is a completely arbitrary standard. The only argument I can think in favor of this is that arbitrary age-based standard is much harder to abuse. But that is a (valid) implementation problem, not a moral one.