The more I read into this discussion the more I think about the stupid fact that our society is based on numbers. (and that's coming from a mathematician.) There are a number of < 18 year olds that are most likely mature enough (heck, some I would have thought were > 18 if I had not asked) but because they fall below a certain number it's "Sorry, you have to wait"
I understand the argument that if they were truly mature they could wait the additional years but there's a number of individuals who are well beyond the 'legal' age involved that are buying for themselves and don't deserve to own a water pistol let alone an airsoft gun. No verification system is going to prevent those morons from getting their hands on guns.
I'm not saying I condone retailers selling to minors and I have no intention of buying from a retailer that would but I wish there were better checks in place to prevent the dumbassery (to coin a term) that gives the community a bad name.
On a positive note I have heard that the cops will try to trace back the sales of an airsoft weapon if it is seized from a minor. This is far from perfect but at least it's something.