I know you've heard this before, but honestly, until he's ready, he's just not going to do it! THink of it like walking. Some kids really early, some kids late, but eventually they will all walk. You can help them and guide them and provide support with starting to walk, but until they are developmentally ready, they just aren't going to. Some people tell you that their kids were potty trained at young ages, and in some cases, maybe they were, but in most cases, I've seen, it's the parent who's really trained. I don't believe they are really potty trained until they go on their own intitiative. They may be able to keep their pants dry all day, but if Mom is taking them every 30 min., they aren't really getting that urge and going. It's the same concept of people that brag that their 1 year old knows the alphabet, but they are just singing a song. THey have no concept at that age what the song means, they are just repeating lyrics like you would "Twinkle Twinkle Little Star", so they don't reall "know" the alphabet. I hope that makes sense.
My oldest son was a really late potty trainer. I got the potty and started doing all the "prep" stuff when he was 18 months old. He was a couple months past 3 before he really even tried. No matter what I did before that mattered. He was 3 1/2 when he started preschool and was just finally in underwear, and even then, most days he had that "baggie" of wet clothes waiting for me when I picked him up. I was so frustrated! I believe it was around Halloween / Thanksgiving before he stayed dry all day all by himself (he was turning 4 that following February). It was a couple months after his 4th birthday before he stayed dry at night. He's now 6, and still has maybe an accident a month at night, but never during the day. I racked my brain and tried every bribery tactic in the book. He really loved going up in the attic with daddy to look at the Christmas decorations, so that worked for a while. I also did a potty present for a few months. I wrapped up a small toy in the bathroom and put a grid on it. Every time he went, he got a sticker, and when the grid was full, he got to open it. I started with 5 stickers on the present and added 5 more to work for with each gift. I am not sure the presents really did much, but he was 3 1/2-4 before I believe he was developmentally ready to get it even though he's a very bright kid.
That being said, I hated every minute of the potty training struggle with my first, so with my second, I kept putting it off. He'd see big brother go and watched Daddy. And he'd go when I'd take his brother in public. I would just tell him good job, and never really made an issue out of taking him potty. Maybe I was in denial because of the stress my first put me through. :) He was still soaking his diapers at night and all day, and I just didn't want to deal with it yet, so I had told myself this summer I'd pump myself up and we'd go for it. Well, one day in January, out of the clear blue, my 3 year old told me he wanted to go potty. And he did. He stayed in pull ups for the whole week and I was still skeptical that it wasn't for real because there is no way it could be that easy. Not when #1 was so impossible. Sure enough, a week later, he never once peed in his pull up during the day or the night. He went completely on his own. I guess he was ready to do it.
I've rambled on now, but the point of my story is to not stress about it now. Your son will eventually go potty. It has nothing to do with intelligence or anything. When he's ready to go, he'll go! Don't let the stress of what other kids do get you down or make you feel pressured!! Every kid is different.