If:
...you are on a mailing list that contains adult content and as an age restriction, and
...you are under the legal age of majority in your region, and
...you find yourself composing a post to said list that mentions said age as part of an argument that there are people who have not yet reached the age of majority who are "mature" enough to be on adult lists,
DON'T POST.
Uh huh. You sing it, sister. You sing it.