So if you really need to discuss it here, in a nutshell, if the depiction is arguably prepubescent, that's when its illegal in many countries and even under certain international laws.
The reason I can post responses to requests is I have a bit. I do not keep anything that I can see reasonably argued as someone not having started puberty.
its more complicated by country and if its a discussion in the thread then that does factor in if you are being very descriptive regarding age and development, but for the most part, the before puberty is what the government or other authority is looking for.
its also illegal to exchange pornography of any kind with an underage person, even if they are the artist.
I hope that covers all that we can in this type of thread; we aren't legal experts. it's just our practical understanding and limited experience.
Hope it makes sense to you.