I have an account there, but honestly I just log in to get the free stuff and hopefully trade it on Flight Rising instead.
Adults do seem to be on there, but they're few and far between from what I can see. Typing is limited to words that the staff have chosen. But the main reason I'm not active there is because you can barely do
anything without a paid membership. Want an eagle? Paid membership. Like the look of that neat apparel item? Paid membership only. Want a cool home? Paid membership. I would honestly say that 90% of the stuff on the site, even some features, are member only. And if someone trades you an item that can only be purchased by paid members, you can't even wear it or use it.
There doesn't seem to be too much interacting involved, but like I said - I don't play it fully, so I might not be the best person to answer this! You can team up with other players on an adventure, or you can go solo.
I'm guessing it could be fun if you have a paid membership, but otherwise, it's pretty boring IMHO.