if these 10-12 year olds with tempers and issues are getting past the forum application and the interview I think that falls on the staff that accept/approve the application and they should be held responsible for accepting unfit applicants. (only this paragraph is a response to korm, rest is toward the age restriction)
An age restriction should not apply ever, as anyone of any age is capable of being an amazing staff member, or the most abusive staff member. In the end the interview and community interactions should give a proper view of the individual and how capable they are/can be as a staff member, not the age or maturity level.
+1 it is not really necessary to have an age restriction, and just makes it harder and adds an extra step for young applicants.
I still believe that an application can be denied for age or immaturity if the community/HAs see the candadite unfit for that reason. But not even allowing them permission to apply without a form of high staff consent is not needed.