That's actually a really interesting point. As I recall, the concept of teenagers or adolescents didn't actually exist until the majority of young people started going to high school. Before that, young people spent their teenage years around adults, doing apprenticeships or working with their parents on the farm or what have you. Teenagers are very much disposed towards copying the people around them, in the past that meant the person teaching them their trade, but with the advent of high school it meant copying other teens. That sort of isolation induced sub-culture is the case of teenage rebellion and counter-culture.
You are right. My husband started working full time in his father's business just prior to turning 13 and previously to that he had worked in out of school hours in his grandfather's patisserie in their home.
I declined the opportunity to stay in the school system and started work at 14 years, though I returned to study 5 years later, when I was ready for it.
These experiences did not hold us back. We never thought of ourselves as teenagers or adolescents - an entirely modern invention. Nowadays the teenage years seem, for some, to go on for decades. And to what good?