That started with age segregation in schools back in the 1800s (age of consent laws were another edge to that sword). That set up obstacles to interfere with older students educating younger students and served to put walls of separation between age groups so that younger students could be taught one thing and older students could be taught something else--educational compartmentalization. The older students would presume the younger students were being taught the same thing. Over time, they could teach "the Earth is a triangular pizza" and "stars are made of molten baby powder" and who would know.
Its amazing how many parents believe "they're teenagers" as an excuse for the behavior of their children when the truth: they're actively and intentionally indoctrinating kids against parents. Feminism: genders as a separate species. "Pop culture" teens as separate species, adult as idiot enemies (started in the 50s, British import).
Once, I went to purchase Acrylic sealer from a store. I was at a location that required ID. Of course, I left ID in the car. I don't smoke or purchase alcohol so why should I carry ID around just to buy art supplies. Well the young guy (prob 18 years old) he said "Well you know people get high on this stuff on parking lots. Someone got arrested for that. You know, we have to be treated the same." So I'm like: "What does someone sniffing art supplies on a parking lot have anything to do with me?" (I use sealer for archival purposes.) So I asked: "If that guy *points* over there murders someone, you get to go to jail too, right?" The look on his face evidenced activation of gray matter that had never been used. I left the stuff, went to a different store and bought it without ID, principles.