I found a small survival multiplayer world that is run like a community project. It is called Anything SMP and the whole point is that the server gets reset every so often.
The community gets to decide what they want to do each reset. It sounds pretty casual and open and it is welcoming for any ages.
The host says they are 14 and they just want people to have fun.
Anything Goes Community SMP Reset
GG.MINEWIND.NET New Server IPVanilla SMP Wanted No World Gen
This is a survival multiplayer world that stays close to vanilla. It is meant for players who want simple Minecraft and not a bunch of big changes.
It allows a few small extras like tree chopping stuff and some furniture. It avoids terrain generation changes so the world still feels normal.
The vibe is chill and it sounds good for playing when you are bored and bringing a friend too.GG.MINEWIND.NET New Server IP