"hoster prohibits nsfw so we add age verification" to change what about that exactly?
if the adult users post adult content you are still getting booted?
age verification is a spicy topic, but, once again:
keep your instances small, only allow registrations by request, and if you doubt someone's age, don't let them in, or ban them later.
on fedi it wouldn't even change much, they'd register elsewhere or self-host to get access to content.