1) thinks that voluntary pedophilia is a thing
2) children can consent to sex with adults (again, broad statement that he didn't even limit to older teens)
That's very different from children experimenting together. Stallman implies that not wanting some adult creep to prey on your kid is just some sort of moral panic, which is... a pretty horrible take and one that is often repeated by predators. A teen having sex with another teen is normal and part of the process of maturing, but with an adult it has a completely different power dynamic.
Plus, being attracted to prepubescent or pubescent teens as an adult is inherently awful and problematic. It has nothing to do with a teen being attracted to another peer.
1) A 12/13 year old and a 16 year old experimenting is likely pedophilia depending on the biology of the 12/13 year old.
2) consent is a circular argument. The assumption that they can’t give consent arises from the assumption of harm and therefore cannot be used to justify harm.
Animals for example can’t give consent to each other, that doesn’t make two bald eagles reproducing harmful.
Especially since the quote was in the context of dutch pedophiles organizing to create a pro pedophilia party. Those are explicitly adults, some were very old adults too, organizing to be able to have sex with kids and teens. It wasn't just him defending teenagers fooling around or sending nudes.
(I added a bit more to my other comment after I posted, sorry about that)
Taken out of context it’s a different story.
The question was about when the younger party instigates. If such contact is inherently harmful then two prepubescent experimenting with each other would presumably cause similar issues. I feel some cognitive dissonance between those two examples which is why I was hoping someone had some actual research on the topic.
re:2) The assumption that they can’t give consent is due to the inherent power imbalance in their “relationship”.
In general power imbalances are likely, but if that the argument then you should talk about power imbalances not age.
PS: Not an objection to downvoting but what exactly do you disagree with here?