It is not a new thing for fashion to be designed around the young, it has always been so, and for several reasons........
The young are at the beginning of learning who they are, literally and figuratively trying on different "styles" to see what best suites them.
They are also learning about other peoples responses to them.
The younger are in mating season......They are doing what they can to find a mate, like any animal of breeding age. They are finding ways to best show off the fact they are good breeding stock.
The young have, percentage wise, a larger allocation of their disposible income dedicated to fashion, if they have no children, mortgage, etc.
Hopefully, as one matures, you have found what best suites you.