S.S.
I would say start now with the good touch bad touch. Let him know that any touch that makes him feel it is wrong that it probably is. I have taught both my boys ages 11 and almost 9 and my now 5 year old daughter that there are good touches and bad toucher and areas it is ok for people to touch and where it is not ok. I also let them know if that happens to go straight to an adult that he really trust even it is Daddy or me for that matter. the way i have taught my kids is when it was bath time and I would wash them up I would let them know which areas are for them alone and no one els to touch we would call them places the no no spots and I would make them wash them areas them selfs unless they were that messy that they needed help. make a game of it so he can have some fun with it in the bath tub. When I help my 5 year old get her bath some times I will ask her where are you no no spots and she will point to them I even include the butt as a no no spot as well. I will tell her ok now time for you to was the spots that mommy isn't suppose to touch as well. hope it helps