Just because your under the age of 18 doesn't necessarily mean you not allowed to have a gun, I'm underage and I own a TM M4 and some shitty ass MP5, I believe Airsoft can be for all ages, if treated respectfully, and civil.
I know people may flame underage Airsofters, personally I do that myself seeing how I'm underage to which is Ironic, but the underage kids I see with Airsoft pretend like they know everything about the sport and everything about guns. They run around with guns shooting things or people and get in shit from the cops.
That is one reason why everyone prefers to have Airsofting for players over the age of 18, but don't feel bad that you have a gun and you are underage, feel bad for smuggling one, if you are respectful to the playing environment around you and players around you then you have the right to have fun.
If you are the type of child that runs around and shoots people and makes crappy youtube videos about "wars" then shame on you, people like that are the reason why Airsoft is hard to get in Canada.
I have no Idea why I just wrote that,Cheers!