I know that several online vendors require you to enter your age when purchasing firearms related items, such as magazines or bayonets, heck I was asked if I was over 18 the last time I bought a can of air duster (do you have to be over 18 to buy these now?).
Since these items do not have any age restrictions attached to them by law is there any reason why you have to provide accurate information?
If you are wondering why I want to know it is because I got into a discussion about this at work, a co-worker said ANYTIME you lie about your age it is a crime (he could not tell me the actual offense). I said that unless there is a legal age restriction on the item the worst the company can do it not sell to you.
And yes if anyone wants to know I am over 21 so this isn’t something I have to worry about.