If you are asking whether 13 is too young to start invisalign, it is not. If he is a candidate for invisalign treatment, and your doctor says he is, than this is a wonderful way to have straight teeth without later on going through the metal bracketts and wires of old fashion braces. Please go to You Tube. Type in: The Winner of the Search for Invisalign Teen 2009. Her name is Sam and she is from Winchester, Mass. Watch her and listen to her story. There are many teen testimonials for invisalign online. Check them out.
I do not know whether your doctor is being over zealous in his recommendation for invisalign, so it is hard to answer wihether it is the proper treatment for an overbite. You mention there is not crowding of the teeth yet, so it sounds as if there will be. It may be an unnecessary expense at this time for you, but your son made need it anyway later on. Either way , it is the best route for all to go who want straight teeth .