I think for the reseller's incentives to stop selling to minors would be potential lawsuits. I mean even Canadian Tire requires 18+ to buy their airguns when they first carried it, you have to show proof of age and register your name into their system. (Don't know if that is still the case) But there must be reasons why they take such actions, and I think airsoft retailers should follow for the same reasons.
But when you look at retailers, I doubt many 14 yrs old kid have a credit card to make these expensive orders online, so probably paid for by the parents. Even if that's the case, parents might take responsibility of their kids' action, but sometimes I don't think parents understand the magnitude of the damage a simple AEG can do if there aren't safe precautions taken. So really, until the parents KNOW what an AEG is and what it can potentially do, it'll be hard preventing kids coming in possession of airsoft.
It'd be nice to educate the general public about airsoft in effort to get them out of the hands of minors and probably does the sport a lot more good in the long run. But somehow I doubt shows like "This hour has 22 minutes" will actually CARE about it until something big goes down. (sad. I know)