Itsame,
My analogy may have missed the mark, but what I meant was that if it's illegal for one it's illegal for all. The law doesn't care if your under 18 or not. Child pronography is illegal because it victimizes children(amoung others). Most of them are forced to do things that no child(or adult) should be made to do.
By seeking out that type of material you are adding to the problem by helping create the demand for it and spreading it across the internet. That's a crime reguardless of your age.
To your question on copyright, it depends what country you live in. Copyright laws vary by country and you'd need to check your local laws. Pretty much anything you could buy(movies, cd's, ect) is copyrighted and you could get in trouble for d/loading them.
For more info
search the forums for "legal" and "child porn". You'll find many opinions.