What you’re describing is only possible on de-anonymized platforms that essentially have “know your customer” type policies where users have to provide some kind of proof of their identity. While I agree that there is value in social spaces where everyone generally knows the people they’re interacting with are who they say they are, I don’t think this is ever going to be feasible in a federated social platform. I think Facebook is the closest thing we have to what you’re describing, to be honest, and I believe Meta has even kicked around having a more sandboxed Instagram for minors (though I don’t use Instagram, so I’m not certain on the details there).
For me, in most cases on a platform like Lemmy, a person’s age is not something I care about. I care about what people are sharing and saying. But then again, none of my interests for online discussion at this point in my life are really age centric. I think there are clearly better platforms than Lemmy if people want to guarantee they’re only interacting within their age specific peer groups.
It’s kind of interesting to watch in open source which projects survive and which get forked and essentially made irrelevant. It basically becomes a referendum on the vision of the original individual or team and how well they’re serving the collective user base. If they aren’t accepting PR’s and competently managing development, they’ll likely be forked. So I’m glad to see that folks are making progress with mbin and I can’t help thinking that its entire existence is probably due to individuals not being able to agree on a roadmap for the platform. If anybody has any info on any drama that led to this, I’d be curious to read about it.