Originally society saw everyone as fundamentally the same with age not being a factor so much as experience and learning. Children were seen as tiny adults that simply hadn't been trained yet. Then as things advanced, children were seen as fundamentally different from adults, with children seen as barely trainable animals that had to be beaten into shape. Things persisted like that for awhile. Then the Industrial Revolution came, and the class of 'adolescent' was invented because factory owners did not want to pay inexperienced workers enough to raise a family on. Prior to that, adolescents became adults at 12 or 13, went to work as apprentices and could usually take care of whatever children they sired.

For reasons that I've not figured out despite decades of study, even though all of the socioeconomic pressures which inspired the changes that came with the Industrial Revolution have gone away, we preserve their practices. And appear to want to extend and expand them, further removing the young from society, etc. The thing that worries me is that there are critical periods of brain development. And brain development occurs exclusively as a result of experience. Remove experience, and brain development halts. And miss the critical period, and that development can never occur regardless of attempts to force it to occur.

Without knowing it, we may have passed a critical period. This is just a personal guess. But it seems 2 or 3 generations ago, parents who were really not entirely mature began raising their own children. As raising children is a very challenging task, demanding a great deal of maturity from a person (refusing to let your personal desire to have the child depend upon you and need you override your duty to turn the child into an adult as early as possible), this results in them over-sheltering their child, depriving the following generation of necessary experiences for brain development, and it continues.