OK, I appreciate your clarification. Now we have a clear point of disagreement. You think menarche is as irrelevant as maternal permissiveness. I don't. Maternal permissiveness is irrelevant because it's about another person, not about the person involved in the sex. Menarche is about the person involved in the sex. It's relevant to diagnosing a perpetrator because it distinguishes pedophilia from preying on adult-looking bodies whose owners aren't ready to rationally consent to sex. (The use of force is another matter.) But the key point of relevance is that menarche is part of a hormonal transition that relates to the onset of natural interest in sex. That's where the necessary/sufficient distinction comes into play. The hormonal transition isn't sufficient to prove that the younger party was interested, but it's necessary. And then the defense could attach additional evidence of mutual interest, and the prosecution could answer with evidence of disinterest, coercion, resistance, etc.

Control of menarche is irrelevant, just as control of turning 18 is irrelevant in sentencing. It's just a baseline physical threshold to which additional arguments and evidence can be attached.

Take the Genarlow Wilson case. If you were a juror, wouldn't it matter to you that the girl he had sex with was 15 rather than 11?