These two are allegedly 20. They sure don't act like it.
Reading this is awkward because the way the author sets it up is that they're children. I know I'm a weird case, but I didn't have physical sensations until I started progesterone when I was 21. So like...this is just weird.
I noped out when they said they are “children” whatever stupid fetish the author has I’m not bloody interested
I'm pretty sure they just meant they're not technically past whatever Japan considers age of majority. It's never been clear just how old those two are, but old enough to know something about being an auto mechanic if I remember right. But it's certainly not out of character for either of them to start concentrating on some irrelevant technicality.
That said, I don't totally buy this. There's something about it that doesn't seem like them. I feel like the aggressor/reluctant dynamic doesn't suit them. I feel like if those two ever did stuff, they'd be half the time talking about totally separate stuff, and half the time being like "OK, what about this? Does this do something?"