Nobody, kid or otherwise has any business shooting game unless they can do it safely without hands-on help , and then comprehend the gravity of the situation once life has been taken. It's not a video game.
It's all a judgment call on the part of the person mentoring the new hunter as to when the beginner is really ready. Like has already been said here.........I've seen kids under 10 who I felt were mature enough to take on the task and I've seen adults who never will be.
In that respect our sport is completely unique. Personal character means everything.