I kind of think it's a cultural thing. Japan isn't as sexually open/expressive as western countries. He also seems a bit isolated from his peers and he could also be a late bloomer.
some people just aren’t interested in sexual stuff. and he’s probably one of those people who is so sweet & innocent that people don’t talk about anything explicit.
They are really cute. Started kind of weird though. How is a 17 year old that innocent?