So if someone tells you that it is illegal to turn left at a certain intersection but you do it anyway and you get caught (How, I'm not sure) making a legal turn, someone finds out you thought it was illegal, you get thrown in jail and go to court, fined, etc for making a legal turn because you thought it was illegal?Touche.
I think it can be construed as being illegal.
Simply:
Dealer can't do it.
I'm aware that dealer can't do it.
Therefore that awareness can be interpreted as "reasonable cause to believe the person is prohibited from receiving or possessing firearms under Federal law."
Also, it seems like the NRA would have teams of pro-gun lawyers and would gladly post it if it were clearly legal. Instead they have "Persons less than 21 years of age for the purchase of a firearm that is other than a shotgun or rifle." listed under "Ineligible Persons" in the Federal Laws section, here: http://www.nraila.org/GunLaws/Federal/Read.aspx?id=60 . So, I guess I'm not the only one who thinks this way.
Either way the law isn't clear. With terms like "reasonable cause to believe" that can go either way.
So, I chose to steer clear of selling handguns to anyone under 21. If, however, I don't know how old you are, then I guess I don't have "reasonable cause".
Obviously that link is at least partially incorrect because I've already showed you the state law that says 17-20 year olds can legally possess handguns whereas that link says they cannot.
That said, I can surely respect your opinion on not wanting to sell something to someone for whatever reason but, until proven otherwise, I can't say that it's illegal.