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?