I would argue that "few people are capable of so on their own at that age" because they were never given the opportunity to learn and practice self-discipline a

I would argue that "few people are capable of so on their own at that age" because they were never given the opportunity to learn and practice self-discipline at an earlier age. After all, the typical American schooling experience allows very little room for deviation from the same thing everyone else is doing. If you started to self-direct at 13 (or earlier), you'd probably be pretty self-disciplined at 18.