I was a Boy Scout and later as my Sons grew up I became a Boy Scout Leader. Boys can join in the 5th Grade and age 11, I think, so 12 is good for a knife but they had to have a bit of training in order to carry one and if they made more than 4 safety mistakes with it, they loose their knife carrying priviledge, and must redo their training. The rules are made clear to them at the start.
- A knife is a tool, not a toy.
- Know how to sharpen a knife. A sharp knife is safer because it is less likely to slip and cut you.
- Keep the blade clean.
- Never carry an open pocketknife.
- When you are not using your knife, close it and put it away.
- Keep your knife dry.
- When you are using the cutting blade, do not try to make big shavings or chips. Easy does it.
- Make a safety circle: Before you pick up your knife to use it, stretch your arm out and turn in a circle. If you can't touch anyone else, it is safe to use your knife.
A SAK is a good place to start or a medium size single blade lockback.