I can't speak from experience but it's a fact that a lot of teenagers prefer to date older people, like 14 or 16 yo dating an University student or graduate... There's even the case of liking people older than that, why? well there's first the attractive look of someone mature and then there's a misconception (that is often right) that all people in their age seem to be too stupid or immature. It doesn't make them feel safe to try making wild things without experience or they don't look very interesting compared to an older person... And in a perfect world without malice, it would be okay to choose that adult instead.
But the risk is too high, so many just want a one night and that's it, is hard know their lies... And then there's the social stigma. The moral pressure always comes from the fact that other people think that you tricked this youngster into sleeping with you, that's why is despised, no one wants to be labeled like that, your life could be ruined and you might even go to jail... And in the case of the teenager? nothing much, just rumors and then they move on. Of course I'm talking about the specific relationship in the range between 13 ~ 18yo to an adult between 20 ~ 30, if you move those numbers it feels like it's a different case imo XD
Aaaaaaanyway, is not worth the risk, and if the feeling is mutual you still need to be responsible and said "wait until you graduate" and that's like 3 or 5 years staying alone! ugghh!! so the faster you teach yourself and the girl involved that love isn't an once in a life opportunity or the concept of soulmate doesn't exist the better, rejecting someone shouldn't be something you will regret for the rest of your life because you don't like giving others the chance.