Humans don't spend 18+ years preparing how to lower a seat post or drive a truck or even do pretty much most jobs. No one is solely training for 18 years to do anything.

Most of those 18 years are having a fucking great time (being young is freakin awesome) and living a great life is never a waste or a negative ecological footprint.

Society artificially slows education down so it takes 18 years to finish school because parents need to be off at work, so 18 years of baby sitting is preferred. By 18, kids are at the age where they will no longer be told what to do so it's off to the next waste of time, college, then 30 years of staring at a blinking box...or whatever.

When I was 12, I decided I wanted to drive a car, I'd never driven a car in my life, but I took my parents car and drove it around wherever I liked with absolutely no issue or prior instruction. I did this for years.

The youth are very capable, we just don't want them to be too capable...