I think this depends on what opportunities are available, and whether these opportunities suit their interest. As for me, I started earning when I was in high school. I have had passion for arts since I was a kid, and through constant practice I pretty much improved and developed skills on my own. Since no one really taught me, I knew how hard it is for people who are just beginning to discover how to work things out. Here comes the opportunity to earn. I began giving art lessons to kids. I also joined several art contests that would get me discounts to art supplies and a chance to join other major art contests. I think when you discover what you really want, you can make use of it to earn money. If you're into music, you can either teach other people or perform in various events.
Another opportunity is the academics. Since I kind of do well in math, I also did tutor some kids in our neighborhood. That way, I don't only earn but also get to review amd learn new techniques.