T.T.
He's still so young, PLEASE don't compare kids. Every kid is different and he will be ready when he is ready. My first son was four before he decided to do it. He showed no interest in pt'ing and would flat out refuse until he finally decided on his own he wanted to do it. My 2nd son will be 3 the end of September and is not potty trained (and niether are the boys of most my friend's boys the same age). He will go when I ask him, but up until the past couple of weeks he hasn't been ready. Like my ped said, they won't pt until they are ready to, if you push it you both will be miserable until he is.
You can buy him a potty and even try pull-ups, but don't push the issue. He's still very young, give him time.