@Sprite I don't know if it would be a HUGE leap forward, but it's a case of might as well.
AFAIK, ActivityPub allows arbitrary fields to be added to the Profile object, so sites might as well add some sort of adult/nonadult tag (maybe not 18+ as ages of majority differ internationally).
It would be as useful as alcohol sites putting up splash screens checking users' ages before they access the website: No, not trustworthy, but checks the box for legal compliance.
And yes, some users might want to have their interactions skewed toward older folks, again yes, not trustworthy, but it would help some.