In Ontario, there's a law that prohibits airsoft under 18, so you'd be out of luck.
In other provinces, it depends. Some have "noob days" that will accept underage players a few times a year. Some hosts wil accept you if you're not retarded.
A few rules of thumb for you:
- Don't say "yo im 12 and im vewy maturre can i play wit ur team???"
- Don't be l337deltasnipar
- Be mature; but
- Don't say you're mature. Show it.
- PM the host and ask him politely.
- If the host says no, well that's it. Don't start arguing, or don't come raging on ASC saying how you're the future of the sport and bla bla bla...
- If you know personally established players (not "forum friends", but IRL), ask them if they can vouch for you.
- If you're accepted... you're lucky. At the game, prove your deserve it. Call your hits, listen to the rules, don't overkill, etc.
Looks like you read the FAQ, so that's a good start for you.