The biology isn't the important bit for the most part, its the mentality.
For example, in extremis, there exist cases on record where a five year old has been made pregnant. She was therefore, biologically ready to reproduce, or at least capable of doing so. But you can bet you bottom dollar that there is no case in which shagging a five year old is either desirable or right.
Biggest age difference I've been with (on the younger end, I've also dated far, far older women, someone in her 50s) was 14. Me..about 19 at the time. Autie chick, pounced on me and more or less dragged me off caveman style. As in 'whack over the head, right, once you've recovered, don't forget to bring me back some tender cuts of Smilodon' I could have said no, legally I was meant to, but it just happened (in this particular case I don't think I COULD have stopped it happening, short of seeing her coming fast enough, realizing her intentions and actually hurting her to stop her doing what she was hell-bent on doing, and that I wouldn't do)
And it went on from there. I really, really, really regret the way things turned out in the end, and that I didn't end up married to her. If things had been different, we'd probably come as a pair on here, and be bitching together about how the kids were playing up last night.
I draw a line between 'illegal by statute' and 'abuse', the former I couldn't give a rat's ass about, the latter I'll have no part in, and if I do sniff it out then the abuser is likely to meet a side of me people rarely see, and that nobody ever wants to meet.
If someone can mentally consent, never mind whether they have hair down there or not, and if the partnership is equal in all respects, and both love each other, I'm allright with it. Does it make me a paedophile? hell no. Officially speaking that particular engagement, would have been viewed that way, but I don't seek out young girls for relationships. If I'm going to get into a relationship, the important thing to me isn't the age, but that both of us are right for the other. 14? 50? either way, if it just so happens that the two of us click together and 'work' then its on, assuming we both want it that way. Otherwise, its either someone else or noone else.