There is no hard and fast rule for a knife being considered a weapon or not. Every locality and state varies.
At the end of the day, knives are just tools. They can be used as weapons if needed, but they’re tools.

I even consider firearms tools, but knives are purely tools in my eyes. Just like a hammer or a screwdriver.

I guess that is just how I was raised.

To answer your question, the proper age to receive a knife is left entirely up to parents. My parents let me have my first knife when I was 7, and I was in Cub Scouts from that time until I was 10(I would’ve made Eagle Scout, but I’m from a town of 375 people in Alabama, and no one there believes in progress, which is why I left). A year later, I was shooting a gun for the first time. It sounds like you guys have drilled safety into his head, which is what my father did to me as well. It sticks. All my guns are unloaded with the chamber open so I’ll know they’re unloaded, and while my pocketknife stays razor sharp, I don’t play with it. It sounds like the police and other people in your town are closed-minded, and obviously don’t believe a boy should be a boy. 4″ and over is usually considered a weapon, and 3 1/2″ and below is not. So, with that being said, it also sounds like y’all are being picked on for no reason. From what I’ve learned, if a boy learns how to use a knife or a gun at an early age, along with the safety, they’re less likely to stab themselves or shoot themselves in the foot. There was a kid I went to school with who shot his thumb off because he didn’t know diddly about guns, and his parents were the type to take him to the ER for a scrapped knee. I’d say you two were being picked on above all else.

I was walking through a big-box home improvement store when I saw a gentleman approximately a decade older than me trying to remove, by hand, a long piece of plastic that had become entangled in the wheel of a shopping cart a lady was pushing. Seeing that he was making no progress, I walked up, removed the knife from my pocket, opened the blade and handed it to him handle first. He very politely accepted it and proceeded to cut the plastic from the wheel. Amazingly, he knew proper knife etiquette and returned it to me in the manner in which it was received.

Then, the amazing thing happened – The lady whom he was helping thanked him, but then turned to me and said, “You remind me so much of my grandfather: Quiet, unassuming, but always prepared. Men like him are hard to find these days.” She thanked us both again and then left.

The gentleman then turned to me and thanked me for bailing him out. “You really helped me save face there. Thanks for letting me use your knife instead of just taking over and doing it yourself. . . but I think you got the girl anyway!”

The Art of Manliness – respect from the men and admiration from the ladies. It’s a win-win.

For awhile I carried a neat little lockback clip knife. Basically a 3 inch long very flat folding knife that had a spring clip on it so you could just clip it to the inside of your pants pocket. Not terribly durable, as knives go, but mighty convenient. I lost it a while back, but I might pick up another of those. Much easier to carry around than a bulky multi-tool knife or traditional horn handle lockback.