Age doesn't correlate with level of maturity.
That being said, we (EU) wouldn't hire anyone under 15, and I believe that applies to the other timezones as well.

Also, a heads-up:
Having "PM me if you need help" or something like that in your status, will not increase your chances of becoming a staff member.
Don't try too hard, it won't look good on you.

Write an application, and leave it at that - that's all you can and should do.