Supposedly, Mamoru would be 17, with all the senshi being 14. Hina would be around Mamoru's age, having grown up with him (then again, she can be slightly younger).
If Mamoru was 18, it would count as statutory rape in the States and would clearly be illegal. I don't know what the laws are in Japan, but if we based it on American standards -- and I doubt that when it comes to reality -- and morals or whatnot, it would kinda be illegal.
It's crazy because prostitution is hypothetically all over Japan, from the stories I've heard. I won't talk about that, though. Trying to keep this a PG-13 rated thread, you know?
Finally done with my 300th post... *sighs heavily*
It's a brain tumor shaped just like the ginzuishou, and Minako's head is going to split open so that Chibiusa can spring forth fully (well, halfway) grown all Athena-like, and then she'll be the 'new senshi' showing up in April, and then they find a mysterious transfer student also named Minako who just happens to be the new Sailor Venus.
It would only be illegal in the US (which isn't where it is) if they were to get down and dirty. Seeing how we usually don't even see them land their punches most of the time I'm not thinking this sort of graphic display of copulation is something the series is likely to do.