Shooting is one thing.. loading them quite another. I've seen 8 year old boys shoot muzzleloaders, but when young people load them in my presence, I watch them like a hawk.

What I might suggest is if the young person is interested. Teach them a class yourself. Get them to the range. Load in front of them and explain step by step what your doing, why your doing that, and what you're feeling. After a few times of showing them, let them try loading under your supervision. Explain to them what they should be feeling. Explain the witness marks, etc.. When you're satisfied, that they handle the rifle properly, then you will also feel better about them doing it without your supervision. Be sure to explain to them that if something does not feel right.. STOP! Make sure you are 100% positive that the rifle is loaded properly.