Who said Lemmy is an adult only space? A huge federation of servers, which strives to be a replacement to Reddit, is open to anyone who wants to be here. So just saying “this is great because there are no young people here” (which I doubt btw) isn’t enjoying an adult-only space, but… trying to restrict a general open space.
(And I’m not even sure I agree with the original statement for a fitting community tbh, I’m rather against such restrictions for spaces.)