I have 4 kids - 3 boys and a girl. My oldest had absolutely NO desire to get out of diapers. Everyone told me to wait until he was ready - well, this kid was NEVER going to be ready. Ever. When he was four years and 3 months old, we finally told him that was it. If he wanted to wear diapers, fine, but he needed to stay in the bathroom as long as he was wearing a diaper. We said that 4 year olds were too big to use diapers and feces belonged in the bathroom so if he was going to poop in his pants, he had to stay in the bathroom. We were very matter of fact about it so that he wouldn't think he was being punished. He was potty trained in one day - he didn't want to stay in the bathroom.
My twin boys were easy, but they also trained later. One trained himself at 3 years old. The other boy had motor delays and we were told to wait with him. When he was 4, we just said no more diapers and put him in underwear. He figured it out very quickly. He was like my oldest, though, in the sense that he was never going to make that decision on his own. He was perfectly comfortable in diapers.
My youngest (dd) was easy, but I didn't wait for her to decide. I knew she was ready when she was 2 1/2 and I just told her she was a big girl and too big for diapers. She trained very quickly and I'm glad that I didn't wait with her. I think she probably would have been like her brothers that were very content with their diapers.
Your son is still young enough that you don't need to worry, but I just wanted to say that my experience is not that kids will decide when the time is right.
Sorry so long. Good luck!
Erica