I said it bothers me in general. I added the part about the full size gun after I mentioned that I'm all for people having defensive weapons. What I was aiming for saying was that it isn't a pistol meant to carry with you, so the possibility he was wanting it to defend his life in case of an emergency is greatly reduced. When I was weighing the possibility of selling to him, I was trying to take that into account to make sure I wasn't depriving a person who desperately thinks he needs protection against a pending threat, the ability to defend himself. Sure it could still be used for home defense, but he could legally buy a rifle or shotgun for that.
Under 21 cannot legally carry a handgun for self defense so that doesn't really come into play.
Your gun, do with it what you want and sell it to who you want. There are some 40 year old men on this very site I won't sell any type of gun to.