J.O.
I'm a firm believer in that it has to be the right time for the child and they'll do it when they're ready. My 1st daughter started showing interested at 18 months and did really well. But after a few weeks, totally lost interest. I don't think there were any significant changes at the time. We tried periodically for months to get her to be potty trained again, using bribes, rewards, etc, but it didn't really matter.
Then, magically, just before her third birthday she was ready and was potty trained during the day within a week or two and only had minimal accidents at night (which was really our fault because we weren't good at limiting fluids after dinner). So I say, let him be. He'll figure it out when the time is right for him. Even though they're little they are independent beings with their own agendas.