You got just about as many answers as there can be, I just want to refer to your saying that you wonder if you should wait until your son is 16. Well, boys grow until the minimum age of 18 and today there are studies saying that they continue to grow until 21-22. So 16 wouldn't have made any difference except that he will be less flexible at the time with less co-ordination between the rate growth of his bones (fast) and his muscles and soft tissue (slow), so I think teaching him now will only help him later on.
As his father, you will have to give the final decision, so don't take any of it lightly, you can always check with doctors (preferably sports related doctors) or find medical articles on the topic. Always remember that 10 years (the article you were talking about) is a long time in medical terms, so try to find if any new research contradicts that information.
In any case, enjoy Aikido!