I kind of disagree? I am gen Z myself, and have used reddit extensively. While I like Discord a lot, I strongly disagree with using it to host content, essentially gating non-members from getting what they want (which is what leads to these communities with ludicrously inflated member counts). And this sentiment definitely isn't just me, a lot of the techie "CS major" people I know lean towards using slightly older services - which is also probably why the aforementioned /r/localllama community still has more than 60 thousand members.

That being said, Discord does have some advantages over older forum-type communities - it's usually way better for cultivating smaller communities, and its no-effort-required chat systems means that you can always hop on and discuss things that are on the cutting edge. This is quite important in a field like AI, where it feels like something revolutionary happens every other week.

(Also, I don't know if that implication was intentional, but gen Z and "underaged" haven't meant the same thing for many years now)