I mean, in the Shota x Gyaru miniserie the boy is...well, that’s a grade schooler.
Also, I’ve seen girls grow fast when I was a middle schooler, but GRADE schoolers like this, never in my life. No sense.
It's fairly rare, but some girls really do develop that early and their childish innocence and directness can result in things like this. They say exactly what they think without any embarrassment that an older girl would have. Think how little kids will happily tell someone they like that they love them, or ask someone to marry them, only with a child that's body has developed early and looks like a teen's body already.
Along with that some girls get interested in romance and even sex (without full understanding of either) at a young age. I have personally seen a 10yo girl (with a pre-pubescent body) basically sexually harassing a guy in his early 20s because she took an intense liking to him. If you want more details:
It happened at a summer camp I worked at one summer. We got new groups of kids each week and one week this girl became obsessed with one of the male counselors. She announced her like of him by sneaking up behind him while he was sitting down, then quickly hopping into his lap. She then refused to get up and started squirming around deliberately rubbing her butt against his crotch. He ended up having to avoid sitting down for most of the week, because she'd repeat that every chance she got. She also was caught twice trying to find a way into the male counselor's quarters. She was given no encouragement, quite the opposite, but she didn't let up the entire week. That was even with the adults that came with her group telling her to stop it multiple times.
All the other adults thought it was funny, including me, but nowadays I understand better just how terrified the poor guy had to have been. He wasn't doing anything wrong, but that didn't necessarily matter if some kid had gone home and told their parents what they saw her doing and it was misunderstood as him doing it to the girl.
This kind of stuff makes people uncomfortable but it really does happen. Ignoring it, and freaking out about portrayals of it does not help anyone.
You know, I kept waiting for a twist like
"Oh, I was just carrying my little sisters bag" or something... But now that there's no twist I'm very uncomfortable...