H.P.
I have twin boys and decided to potty train them a few weeks after their third b-day when they had 3 weeks off between camp and school. I waited until 3 (like I had done with my older daughter) to avoid any control issues by doing it too early. Well, one of the boys was potty trained in a day. As soon as I took away the diapers, that was it... he was trained. Never had an accident and even at night, his pullup was always dry. (He happens to be anally neat too!) Well, the other twin was a different story. He wanted nothing to do with the potty and nothing we did could change that. He'd just sit and sit on the potty and cry and have tantrums and then pee in his pants. It didn't matter to him that his brother was trained.
So, after about a week of trying, I just stopped. I gave him back pullups and sent him back to school w/ the pullups on (luckily, his school allows kids to go w/out being potty trained). I waited another SIX MONTHS until February vacation week and tried again. After a few accidents the first day, he was trained pretty quickly. Still a few constipation issues with poop, but it happened quickly.
So the moral of this story is that he may just need more time. I did not want the whole fighting/power struggle thing so I just waited and luckily by 3 1/2, he was ready. So maybe wait a little longer. I know you'll have friends who say "he's STILL in diapers????" Don't worry about those people... ignore them... Good luck!