Wow! Let's just ask a tough question
Is 16 too young? No and yes. So many factors come into play with a question of this magnitude. The real answer lies in whether he demonstrates the capacity to restrain the temptations of wreckless behavior when riding and whether he is qualified. I personally would encourage him getting his license and taking the required courses for doing so if he shows he is mature enough to handle the responsibility that you are giving him. However, if his current behavior is wreckless and untrustworthy, then the answer is no, not at this time.
We can only instill so much in our children as they grow. If you did your job of training him correctly in the beginning, then there is no problem with him getting his license. Ensure that he understands that riding is a privilege and that the first hint of improper riding you as the parent will remove those riding privileges. It is never easy letting your child loose to do something that can be dangerous. But it is also rewarding for both when he sees the trust you have in him and the excitement that he will experience while riding.
It doesn't hurt to gain the experience at a young age when quick reflexes are a plus.
All but one of my children ride and have been riding for years. The youngest (kirbykajin) is now 26. I am still anxious when he and his wife go out riding, but I am still excited that they share in the experiences that my wife and I share in while riding. It scares the **** out of me when he is one up on the CBR. But I have to lean on the fact that I did my best in teaching him safe riding practices to the point that he is lecturing me in my riding skills.
I personally got my license at age 15 and had been riding for several years before that. Four years later I got my pilots license as well. I always wanted my children to have the same opportunities to experience life as I have. It is never easy but it will be something that can bond the two of you even moreso as you share your experiences together.
Oh and the main thing is. Be sure you are prayed up each morning. Never, ever underestimate the power of prayer!!!