I think that children used to be independent much earlier before humans invented agriculture. By your mid to late teens your body is developed enough to survive on your own and have children of your own. The evolutionary advantage in a hunter-gatherer society of making parents miserable is encouraging offspring from separating from their parents to start families of their own and not compete for the same resources. You see it with all kinds of animals.

And if I'm not mistaken it wasn't at all unusual until fairly recently for daughters to be married off and for sons to start an apprenticeship in their late teens. Only the necessity for decades of education for getting a job keeps children dependent on their parents so long.