I'll give may usual reply to this question and say that if you're asking, then it's not going to be accepted.
Generally speaking, the sort of people that ask are generally looking to get as close to the line as possible... actually, they're aiming to cross the line - but at least know there is a line. If people are looking to push the boundaries, then they are kinda missing the point as to why those boundaries exist.
So no time travelling 90yr olds inhabiting their own 8yr old body. No 6,000 year old godesses who cosplay 12yr olds.
(Probably) No 19yr olds who look 14yrs old. No "Here's a photo of the 22yr old I based my model on - so it's okay".
The rules say:
7. Content (a game, image, video, story, animation, etc.) depicting nudity or sexualization or sexual/erotic activity involving prepubescent character(s) is prohibited. A "prepubescent character" is one that visually shows no sign of puberty, or if non-visual is otherwise clearly intended to represent a prepubescent character. 2D and 'unrealistic' depictions are generally looked upon more favorably. As this involves some discretion, if you are unsure ask a Staff Member.
Everyone has their kinks... vive la différence. These aren't really people, they're just pixels - and so players really need to recognize the difference between fantasy and reality. BUT... you know...
kids.
I suspect the answer is really "it depends on context". If the story hints that the author really wanted this "18yr old" to be 13 - expect a ban. If the story offers no hint that the petite flat chested almost androgynous female is anything other than a clear adult working a 9 to 5 job - expect
(slightly) more leniency.
As to how to contact the staff...
Create a ticket (it's on the main menu bar) or reach out to one by name.