An EU Green Paper is nothing like a law or directive. It‘s more like a basis for a discussion. Like ewald23 wrote (and I remember that, too), there were nude minors in German magazines at least until the 2000s. As I wrote earlier, I guess it‘s not a question of law but more of taste or social acceptance that there are no more 17 year old playmates.
Apart from that, the mentioned Green Paper deals with access to media and is not about minors shown in media.
I only brought this subject about because I clearly remember some mid-90s news in the Netherlands that minors would not be allowed on PB anymore because of some EU law, and the van Breeschoten twins (17 yo Playmates) were the example given at the time (like "they were the last" or something). But I'm not German, nor have I ever lived in Germany, and I really don't know how EU laws work, so, if what I said was wrong, I apologize.