Welcome to Subeta! I do believe a large group of users are 20-somethings, of not older, of course we still have younger and much older users from students to grandparents, but personally I think the demographic is older here.

The main rule difference between here and Neopets is that we do NOT allow multiple accounts per user, there are ways to get additional pet slots/change username etc. so there is no reason to need multiple accounts - so we have very good user clarity/(and in my opinion at least, a better community).

The rest of the rules you can probably look up as you go, or if in any doubt - you're always welcome to file a ticket (Personal - Tickets on the top nav bar), we have a fairly fast response system (normally within few hours, but definitely within the same day)

Useful Links:

What to do on Subeta? Useful general information for newbies Finding friends (Chit Chat) SubetaLodge (Offsite item database, pet colours etc.)
FAQ Site Event: See Omen Islands