Let's qualify your remarks, Prohibitionist.
In my personal experience, at 13 I believe I had the wherewithal to consent to fucking an 18 year old big titted hussy. So, there's one person that had the wherewithal, thus refuting your claim.
You on the other hand, at 13, may have been hoping to soap
@londonfog sweaty ass in the shower after playing water boy on the Junior High football team. Or maybe you were still pulling your tiny pud in a vain attempt to stick the National Geographic pages together. Who knows?
So, while I don't think every 13 year old is capable of making an informed choice, nor do I endorse large age differences in sexual partners (cultural and personal bias of mine) I believe it is possible two people could be the same chronological age and one could not have the same mental capacity as another.
Of course people of different ages have different mental capacities too,for instance your peak mental capacity (assuming you have ANY mental capacity here...big stretch on my part) is roughly equivalent to a toaster.
Can a toaster consent to sex? Hmmm.