The girls are all in their last year in high school.
You could, quite easily, debate that even if they *aren't* cannonically 18, that they are mentally capable enough to have consentual sex with another person in their age group.
Those type of laws are targetted at people who are whacking off to Bart and Lisa (cannonically 10 and
fucking, or quite obvious lolikon.
If you're not a paedophile, and don't have terrabytes of CP on your hard drives, then I think you'll be fine. having one game that happens to have sexual content probably won't even raise any eyebrows beyond the "People actualy read this?" ones.
If you're ultra-paranoid, then use a torrent with encryption turned on.