Any successfull boys potty trained by 20 months?

There's no harm in trying. You can always stop when and if you realize that he simply cannot do it and then try again later. I started potty training my son at 21 months and it took a while but we never went back to diapers. He's 26 months now and still has some accidents, but for the most part he does very well. It's possible that your son can do it with a little bit of patience.