Paranormal Witness Wiki

I need user for Paranormal Witness Wiki.  But there is a but in this.  I do not need unregistered users.  You the show was meant for teenagers from 13 and up.  And the show is for a mature audence because the stories may scare or shock sensitive users.  So my biggest problem is if a unregistered in is under the age limit.  So I need a program to prevent unregistered user to edit the site.  I prefer registered user because than I know they are over the age limit since only people 13 and over are allowed to edit on wiki sites.  So please anyone help me.