There's probably not an age requirement on here. Btw I was in the same situation as you were. My parents hated me attending video game tournaments since they thought it was just a waste of time even it were 5 miles away from me. So I basically gave them a deal, if i don't get top 3 in my first tournament I attended, didn't get money out of it and didn't keep my grades up while I was practicing that I would give up trying to compete. I was 16 at the time, got 2nd place a local tournament at irvine and got $75 out of it.
The next tournament I wanted to attend was in pasadena which was for a CGS qualifier. My parents were a bit skeptical at first when I told them If I won one of their two qualifiers that I would get paid $500 and get to attend the CGS combine at the time. (I wouldn't been able to audition though due to players needed to able to be at least 18 years or older to play) They thought it was a hoax that a tournament would pay that much, but I gave them the same deal like the first one, knowing that I would have to play a lot of better players here than in my first tournament. I got 2nd in the first qualifier and lost to HighGuy. I got 1st on the second qualifier and beat out DOA5. In the end of the day, I was paid the $500 in debit card form and my parents finally gave in that I actually can make a bit of money from playing tournaments.
Oops that was long. Overall, just take it step by step and try to convince your mom that you want to try out and play a local tournament around your area when the game comes out. If you think you are good at the game, you could make the same deal with your mom as i did with my parents.