Mastodon nuked my account again.

This time the reason was that I was allegedly "advocating underage sexual activity."

which is a little bit silly. Underage for sex in Germany is 13. Underage for sex in California is 17.

So what rule are they using exactly?

Most of all I never advocated any activity at all. I just stated the fact that teens have been having sex for all of human history. (but that statement is now taboo.)