You're right about cutting brush being an OK way to spend ones life if thats what one wants.

On the other hand, a year or two in one's early twenties spent cutting brush (or serving in the military, or stocking shelves at the grocery while trying to make the rent each month) in ones early twenties can sometimes ignite the passion for education and self improvement.

Or even trying to make it as a musician.

The important thing at his age is not necessarily what he does, but that he do SOMETHING, and that he be responsible for himself. He's at an age where he can experiment, try, fail, and learn without a lot of consequences.