If your son has a good nature and temperament, then it's okay maybe around seven or so. If your son is too hyper or lacks self control, or exhibits other characteristics that indicate he is not ready for a pocket knife, I think you should be able to identify those shortcomings. If you know your child can handle the responsibility (regardless of his age), then I think it's okay. If you know he can't handle the responsibility but you give it to him anyway, then maybe you shouldn't have the knife either.