Legally, you can sell the gun to this 19 year old provided you are sure he's 19 - but of course the issue here is not *can* you, but *should* you.
I think that if you're prepared to take the time to go with him to try the gun out, you both get something out of the meeting - he gets to see if the gun is for him, and you get to check that he's not a danger to himself or others thru' negligence or stupidity.
Beyond that, it's down to whether you look at the situation and feel comfortable about the kid's morals and motives. If you feel OK about the sale, OK. If not, decline to sell it to him. Ultimately, you have to be able to sleep at night once the transaction is done.
We can't easily give you advice on whether you'll feel OK or not - only you can make that call.
I think that if you're prepared to take the time to go with him to try the gun out, you both get something out of the meeting - he gets to see if the gun is for him, and you get to check that he's not a danger to himself or others thru' negligence or stupidity.
Beyond that, it's down to whether you look at the situation and feel comfortable about the kid's morals and motives. If you feel OK about the sale, OK. If not, decline to sell it to him. Ultimately, you have to be able to sleep at night once the transaction is done.
We can't easily give you advice on whether you'll feel OK or not - only you can make that call.