the other kid/knife question was fun..this one is tough..
i could say that a kid who is moody and stays in his room playing computer games is not ready--BUT the gift of a knife may show him that he is now seen as a trusted and ready for real "grow-up" sort of things and help him move along to adulthood--OR on the other hand the "good kid" may get his hands on a knife and turn into a hacker and stabber..whatever you do make it a real knife and not a "survival" "military" weapon and watch him like a hawk to see how he handles this new responsibilty...