I've thought about that too... I'm sure most have.
Instead of just age verifying... maybe we should do intel verifying. Do up a quick 20 questions or something, make it so you can't take the test for a week, or (if possible) until they read all the FAQs...
1. Where can you find guns for sale? (multiple choice/answer)
2. What is the best gun? (trick question)
I can't think of any more... maybe after I sleep some.
I like the original idea too though. You volunteering?
"War must be, while we defend our lives against a destroyer who would devour all; but I do not love the bright sword for its sharpness, nor the arrow for its swiftness, nor the warrior for his glory. I love only that which they defend: the city of the Men of Numenor, and I would have her loved for her memory, her ancientry, her beauty, and her present wisdom. Not feared, save as men may fear the dignity of a man, old and wise." - J.R.R. Tolkien