How Do You Convince Your Mom To Let You Have A Facebook If You Are Only 12?

Facebook doesn't allow users under 13. It's in their Rights and Responsibilities:

Registration and Account Security
Facebook users provide their real names and information, and we need
your help to keep it that way. Here are some commitments you make to us
relating to registering and maintaining the security of your account:
  

1. You
   will not provide any false personal information on Facebook, or create
   an account for anyone other than yourself without permission.
   
2. You will not use Facebook if you are under 13.
   

There are laws prohibiting online sites from making information about people under 13 available on the Web. Since Facebook is a way of posting information about yourself, they have to abide by these laws.

Tell her you're only one year away and that you're very responsible [if thats true.]

Same issue ...im 12 to...no hope in getting a facebook!!!!

Let her know that you will be safe and responsible with it .And give her time,she ll need a while to think about it. Dont be too pushy or she really not let you .reality is,you wont get every thing you want!