It depends on the maturity of the kid and whether he views such things as toys or tools. I was a a small primitive skills gather and there is an 8 year old boy there and he has a 8" Gerber Bear Grylls knife on his belt and he is scraping wood to start a fire, and he is doing all sorts of stuff. He started all the fires for the camps that weekend himself. I have known him for several years and he always had this knife. When I first saw it I thought he was awful young. So this year, half pullin his leg and wanting his reaction I said "Billy, What is an 8 year old like you playing with a big knife like that." He looked at me real serious like and said I am not playing with it, I am using it" It was the best answer he could have given and I was quite impressed with the awareness he had for his tool and what it was to be used for. All weekend long I never once saw him use it in an inappropriate way. He was way ahead of my boys who are both 10 and I would not give them a knife like that to carry. But he proved himself to me he was worthy. Your own kids will need to do that also. You know him best tho.
So I think it is all in how they are taught and get used to using. You know him best tho.