The risk of damaging the plane has been discussed here before. Unless it is a 4 seat puddle jumper the chances of a firearm round disabling the plane is virtually nil and even in most puddle jumpers it is unlikely. It would take numerous spots in exact locations to do it.
Touche, salesman. Point taken, guns should be allowed everywhere
I also agree with you on minor's. It should be the parents' choice what their children own. That being said, I still think they should be allowed to carry if their parents' sign off on it.