The show appeals to "older" fans, mainly, for the same reason it appeals to kids. It's an enjoyable and well-crafted show, with likeable characters.



It's just that the older fans are Also horny, so their imaginations go to "certain" places.



It's basically the same phenomenon of sexualizing anime girls.



It's mostly harmless, as long as it doesn't go too far, and as long as certain materials are kept behind maturity filters for the sake of the kids.