This ambiguity even makes it worse. So, a "normal" 20 yo grown up can't have sex with a 15.5 year old, but mentally challenged 40 year old can, since he's "of t

This ambiguity even makes it worse. So, a "normal" 20 yo grown up can't have sex with a 15.5 year old, but mentally challenged 40 year old can, since he's "of the similar stage of development and maturity"? You see where that's going? Someone is going to arbitrary decide who can sleep with whom? Also, what is wrong with teenagers having consentual sex with adults? That might not be moral by your standards, but why do you try to push your standards to others? You don't want to do it with teenager, it's ok, don't do it. I don't want to do it with the same sex, but I don't say that's immoral or that it should be forbidden. Don't pretend that teenagers are somehow "not ready" for sex because you think that it's too early. Every living creature on this planet can have sex the same moment when it's physically ready. The nature sorted that out already, and there's no teed to put some arbitrary constrains over that.