Thanks for the input so far.

Izzy, for any question related to knives that ends in "he'll end up cutting himself," the answer will be an easy yes. If you use knives, you will get cut. If I give my son a knife, he will cut himself with it, just like he scraped up his knees riding his bike.

I guess if you're looking for an underlying question, it would be "How old do you have to be to learn to use a knife responsibly as a tool?"

Does he know right from wrong in most situations? Yes
Does he understand the difference between reality and TV/Fantasy? Yes
Does he understand that a knife can cut you and that cuts hurt? Yes
Does he show an interest in the outdoors and in using a knife as a tool? Yes
At six, is he too young to "own" a knife? I don't know