This is not a Federal issue, Brian, but a rather a Provincial issue. Not all provinces have this on the books, but most do, somewhere. I've found the best resource for such info in Alberta has been via the Fish and Wildlife branch of the provincial government. They regulate hunting activities, and lay out regulations for minors who hunt, use weapons, which weapons can be used when for hunting, etc.
But, the Federal law is vague on the EXACT placement of airsoft or other airguns that aren't directly regulated by the CCC as far as possesion and use legislation is concerned. It would be reasonable to assume that if you had to go to court, an airsoft gun would be treated as any other weapon when used in the commision of a crime (and it is so noted in the CCC), but the question is determining the crime. Many municipalities forbid even the possession of airguns within city limits, while others don't, but will prohibit their discharge.
It's a complicated issue, and varies from province to province and municipality to municipality. It's best if you try to find out all local ordinances yourself, but how many 15-18 year olds are going to do that? I like the idea of promoting an "18+ because it's the law" policy as a failsafe to ensure that no matter where you are, you should still be legal. It's not the most technically legal stance, but it serves a purpose to the community at large that outweighs it legal weight for accuracy.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.