What is a good age for a child to get his/her first gun [ pistol ]?

I know many people get their kids motorcycles, ponies, quad runners, etc when their kids are as young as three years of age, but I think for all practical purposes that is too young for a child to have a gun. The size and weight is such they couldn’t be safe with it. Depending on the pistol I think at age six a child can handle it decently. What do you believe the minimum age a child need be to handle his/her first pistol, and be able to use it effectively under adult supervision?