I taught my daughter to shoot a .22 revolver at 8 years old. I know it's backwards to learn handgun first and long gun second, but that's how I learned, and we both prefer shooting handguns. We both eventually got seriously involved in Cowboy Action Shooting, and she won state championships in the Junior division two years running.
I am an NRA instructor, and certified by the state police to teach CCW courses. I am often asked at what age kids should begin learning about/using guns. I answer by asking at what age would you let them use power tools or a power lawn mower? It's not about age, it'a about maturity and common sense. My brother is 11 years my senior, and I'd never let him handle a firearm. I'd never let him handle a circular saw either though.
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It's not that life is so short, it's that you're dead for so long.