I am going to give you 7 reasons to wait. There is only 1 reason to teach him now, he will get outs using it.
BHD is correct with the ASMI studies, they do not cause problems. Throwing them wrong does. (Reason number 1) Overuse is the primary culprit on arm injuries more on this later.
I disagree with JD because on teaching a curve early since it will hinder the development of the FB variations. (Reason 2) Pitchers need to learn how to be successful throwing only a FB (which should be thrown 60-70% of the time) A good change is one of the most difficult pitches to learn to throw well and it takes a long time to master. (Reason 3) Additionally if they start throwing a curve they will not develop the proper mental approach of trying to find bats while pitching. (at the pitchers location and speed) they simply won’t do it and will go to the curve for the K’s. (Reason 4) In this process they will focus on getting K’s instead of focusing on getting outs and keeping the team involved (Reason 5). In the process of getting K's he will drive up his pitch counts. Reason 6)
Once they develop good command of their FB’s and CU’s then move on to the curve. A curve is one of the easiest pitches to learn once you have mastered a good FB and CU. (Reason 7)
If you are interested in the short term success of your son go, ahead and teach him to throw one (by a knowledgeable instructor)/ He will be successful with it, but there is absolutely no question in my mind and most others who really know pitching that you will be hindering his long term development. Maybe only a little or maybe a lot but you will hinder him long term.
I have given you 7 reasons why to wait and I am sure BHD or JD and others will say their sons learned them early and have gone on to pitch well at higher levels, which may be true, but I think you should think it through and weigh the positives vs the negatives before you head down that road.