I wonder the same thing as OP. I work in a school, elementary and Jr high. Every day at lunch I hear what the other staff, almost 100% female, talks about. Such stupid shit, like you'd think stereotypical teenage bimbos talk about. In fact, I would say they're not really talking about anything. None of them seem to have any hobbies. And I don't mean like making model airplanes or some shit, I mean none of them seem to even watch tv or movies. Occasionally someone will try to bring up some show or movie or book, usually one of the few males that work there, and the women have never seen or heard of anything. Even books, and they're fucking teachers. You know what they do talk about now though? Youtube videos. All they fucking talk about is youtube videos. Grown ass women. Some of the younger ones even talk about lets plays and shit. The few times I've been dumb enough to chime in and try to talk about the game, they all say they never actually played it. Now, some of these women do talk about their kids, and I get that having kids makes you busy, but most of them actually don't have kids, at least the younger ones, and they just still seem to do nothing but go on youtube all fucking day, and going out with their boyfriends and shit. But even then, they're going to sporting events or whatever that they clearly don't give a shit about. When they talk about it it's like they weren't even there. Mentally, I suppose they weren't. They were just pretending to like it to try to seem cool to their boyfriends.
But the students at the school aren't like this at all. Plenty of them do have real interests. Some play vidya (like actually play vidya, not that fucking casual big bang theory shit adults do), a lot are on sports teams and actually watch sports (yes I'm still talking about girls, specifically), and all of them actually watch (as in genuinely enjoy and experience and think about, not let their eyes gloss over and sit in front of a screen) different movies and tv shows. A lot of them get really into certain novels, some even read comics. A surprising amount are weebs and into anime.
But practically none of this applies to the girls in the highest grade in the school, eighth grade. By this time, they are beginning to become adults, physically, and mentally. And already I can see that by that age they're all quitting their sports teams and don't watch as fans anymore, they've all stopped reading everything that wasn't assigned, unless it's some meme novel like hunger games or whatever. When a new movie comes out, a lot of the kids from all the different grades like to talk about it, and somehow, the older girls have less insight than the damn kindergarteners, because they weren't fucking paying attention. It always turns out they only went because all their friends were going, and not out of any genuine interest. They all stopped watching tv except maybe some reality shows, but mostly all they talk about is fucking youtube shit, just like the adults. It's terrifying. I haven't worked there for super long, but it will be painful to see girls who actually seemed like fully fledged people with real interests and real personalities turn into these soulless automatons the older ones all seem to become.
tl;dr: younger girls all seem to have actual interests and hobbies. Adult women, and even most as early as jr high, seem to lose all interest in anything except socializing, and letting their eyes gloss over in front of mindless reality shows and youtube shit. Even simply watching tv or movies seems too taxing for them. What the fuck happens to them?
Oh yeah there are still some weebs in eighth grade but only the fat ones.