https://opengameart.org/forumtopic/nsfw-content

I guess that should help with the answer.

If I missunderstood the question and you actually meant to ask if the declaration of works by an underaged creator as public domain or other liscense by this underaged creator would be legal/binding, than I guess I actually never thought about that.

I would think a lot of the contributors here are not legally of age, since the topic of games usually appeals to younger crowds.

Maybe there exists some kind of a grey zone, but technically underaged persons aren't able to declare legally binding facts.

As long as you post something usable, there is no age limit, though they say the site content is unofficially rated PG-13.

I guess what Umplix says is the practical approach that seems to work because nobody asks questions, but legally it could be more complicated. Depending on the minor law of your country.

I guess in theory a minor could upload something, it could be used by a commercial project and the same minor could declare the upload as not public domain because of the age the contributor was, when he/she/they uploaded it.

Seems like a problem to me if you really go into such cases. Technically I guess it will never happen or maybe once in a lifetime, but in theory it is something to think about.

Yep, there's no age limit to posting art, you can do it if your're five or fifty.