Regarding the sex stuff, I remember when 14-sai no koi also started to brooch this topic towards the end of the manga. Imho, any author worth their salt who is trying to write a relatively 'grounded' middle-schooler romance will touch on this subject because it's completely normal. Different cultures have drastically different views on when and if teenagers should be exposed to these topics. In my culture (east europe) 7th grade (so around 14-15) was exactly when sex started becoming an important topic and students started experimenting. Parents were very encouraging about it too and saw it as a natural thing to let the kids 'discover themselves'. And it was so culturally accepted that sex-ed classes were happening around this time too.
I remember having discussions about this with some Indian friends many years later and they were shocked, because where they grew up, guys weren't even approaching girls in school. A very different culture. But, imho, Japan is definitely more in that european mindset of 'enjoy youth for what it is' during pubescence. It's nice that they talk about it, if anything and people should accept these cultural differences.
The one thing that is important is that whenever authors go for this sort of plot line when it's in this very early teenhood is to be careful about how they handle it. Lots of responsibility on the author here to deliver the right message to the young readers. Like for our boy not to pressure Yamada or vice-versa. Big part of why I really enjoyed 14 sai no koi when it came to this narrative, since it handled it with extreme care. Knowing how this manga has been written thus far, I've zero fears that the author would mess this up. The writing has always been extremely respectful. (weird sentence, ik, but you get what I mean).
Not that I think this will go anywhere yet regardless, neither of them seem ready yet. If anything, they might have a moment and then catch themselves pushing too far and just say "wow, I don't think we're ready for this yet, can we wait?" And that will be a perfect message to deliver to the reader to not rush these things if they don't feel ready and just take it at their own pace, coming back to the subject another 100-200 chapters later.
