There are things that one is never too young to learn. Among those, are fixing stuff and killing people. I bought my nephew toy power tools because he's already four, so he's old enough to tackle some rudimentary home improvement projects.
"Okay, I'll make you a shed, but I'm a union carpenter, so I gotta overcharge you, even though you're family."
I have fond memories of going hunting with my grandfather in Argentina when I was a little five year old. I remember when he killed an animal and ritualistically rubbed some blood on my cheeks to honor the occasion. I cried when he did it. But not because it's terrifying to a five year old to watch an adult kill something in front of you and wipe his bloody hands on your face. I was five, but even then I was too much of a man to cry for no reason like that. I was crying because, I, like, uhhh, pulled a muscle when I was uhhh, working on a transmission or something. What?
Anyway, I used to think that five years old is kinda young to teach a child how to kill something, but apparently I was a late bloomer. There's a guy in Illinois who got his son, Bubba (no, I'm not making this up) a license to own a gun. Bubba is 10 months old, by the way. You can read about it Here.
I have no idea if li'l Bubba can fix stuff around the house, but if he can handle a gun at 10 months old, I think that makes him an honorary ninja.