I know this going to sound dumb, but are you sure you clicked save? If so try logging out then in again as sometimes that activates changes you have made. I have only ever seen underage users recently with completely blocked profiles, but seem to think that may not have been the case a year ago.
Unless you specifically block them, you cannot :(
I think they WERE underage and changed their age to appear older anyway that is what I read somewhere here before.
idk but as to your last question it said page not found