My earliest memory is falling off the back porch. I was four years old at the time. Comparing notes with my friends tells me that four is about as far back as our memories go, and that our earliest memories tend to be things that break the flow of our daily lives. It would be fair to call many of them traumatic memories.
This week another child got an early traumatic memory. He is five years old, and he just killed his two-year-old sister. The rifle he used is called a Crickett. The news stories say it was given to him last year, which could mean last Christmas or when he was four. While crickett.com appears to be down for maintenance (or perhaps a comprehensive rewrite), one of the cached pages says: "The Crickett rifle is ideally sized for children four to ten years old..." Obviously the manufacturer does not feel that four is too young to possess a rifle. As for their claims that their products teach kids safe gun handling, in this case they demonstrably failed to teach either the child or his parents the first rule of gun safety: the gun is always loaded. When you shape your hand like a gun, point your finger at your sister, and say "Bang! You're dead!", she isn't. When you use a real gun... well, there's a reason they're called deadly weapons.
You can't buy liquor before you're twenty-one, vote or serve in the military before you're eighteen, or get a license to drive a car or pilot a plane before you're sixteen. Before age thirteen there are restrictions on what you can do on the Internet. We do not expect mature judgment from children, and our laws reflect that. But you can own a gun at age four, the age at which you are forming your earliest adult memories.
I am not against responsible gun ownership. We had cap pistols when we were children and real guns when we were old enough to understand that they were not toys. But in our household the guns are stored in locked boxes and the swords are on shelves above my head. We don't leave a weapon propped in the corner where a child can get at it. We feel that a child is not able to use a gun safely without very careful adult supervision.
In a few years this boy probably will not remember the person who was his sister. But shooting her will always be one of his earliest childhood memories.