bootsnall.comhostelworld.comhostels.comalot of these places have reviews. some hestels have age limits look for those. generally a HUGE hostel with NO age limit is where you'll find nothing but 16 year olds and 60 year olds, very annoying. there are many chains like this. check the reviews man.
pic related hostel I stayed in in amsterdam. (protip: fun hostels' lobbies double as a public bar)