I used to play on an adult only whitelisted minecraft server. It was setup in such a way that day-to-day gameplay was as close to pure vanilla survival as possible. Of course the adult part is really hard to enforce so the owner took a very interesting approach to it. Anyone could join the server but you would be put in spectator mode i.e. be unable to interact with anything but just tour the builds. Then you'd have to make an application that would be manually approved between 24-48h later. Just that delay was enough to weed out the impatient.

See the problem was not about the age specifically but rather childish behavior. So by realizing that we targeted the most obvious one( being impatient) and had great results.

So yea, making something deliberately harder to use might be just enough.

Just make it deliberately inconvenient for normal schlubs to use. CLI-only BBSes for life.

I know you are making a joke, but a barrier of entry is definitely part of the equation here. Right now, a good portion of the web development seems focused on removing friction as much as possible.

USENET, with a proper client, sat on a wonderful local maxima for usability and usefulness, and technical complexity to weed out the riff-raff. I miss those days.

Now I know why the gopher / gemini project exists.