For adults only we have min_age and the gender is not necessary. Again, it’s not about public buildings. It’s about private homes, where those tags are used. So if you think users_boy and users_girl is necessary to have, please explain how to identify a private home having such a property.
Unfortunately the mapper of these objects apparently does not want to participate in the disussion here, although invited several times. Anyhow they have given a detailed reply in the CS-discussion as linked in the first post by Mateusz. Please feel free to have a look there.