If Bare Mettle blatantly says "No children", then I can assure you that there will be no sex. I'm guessing Bare Mettle is aiming for a "T" rating.
But, but! But if there are no children therefore there was no sex therefore there shouldn't be elderly people because they would be younger people's parents and as there was no sex then it's impossible. Or are younger people found in cabbage at the age of say, 18? I'm joking, of course.
However Bare Mettle will have to think about Sui Generis rating sooner or later, and I just want to help by defining the limitations for further use. So, no children=no killing them, no sex=lower rating. What about nudity? Showing nipples on females' breasts will up the rating tremendously even without sex. People will try to undress their toons the first thing they are in game; it's just human nature (I will try to do so too, just because). With physics the engine has will underclothes be a texture (therefore unmoving whatever you do) or will it be like armor? A layer that we can remove and put on. It's a serious issue for, say, younger part of Sui Generis' possible auditory. People love when there is this level of nudity, at least bare breasts, it's what makes a game more mature in their opinion (a little bit off-base if you ask me, but still). However if we're talking about bare upper torso then it'd be only logical to give an option to remove panties/loincloths. Going halfway while positioning SG as a low fantasy game won't work. So I suggest for lower rating go for no nudity, or if you don't care about lower rating - full. Though it can easily be an issue if you're going to make a playable multiplayer (not only LAN), because there will be people who will be offended if someone they play with suddenly removes their character's clothes ant starts to run around naked.
Another issue I'm curious about - did you think about animating breasts movement when characters are wearing clothes (not heavy/stiffing armor). Like Tera Online did. Well, not quite like that game of course, what they did with females' breasts was quite unrealistic, but still. If you're talking about revolutionary physics considering muscles movements why not make breasts move too. It looks really natural when done right.
Nope, I'm not a pervert (well okay, maybe a little bit).
I just want to set limitations.