I have 2 teenagers now and I can tell you with certainty that he will eventually be trained. Don't stress yourself out over it. Don't listen to all the other parents tell you what stars their kids are and how they're training for the olympic toilet training team. There's SOOOOOO much pressure out there. He will train when he's ready. My son could barely put together a sentence so I thought it would be forever before he trained. All my friends around me were bragging about how little "susie" and "johnny" were learning to tinkle on their porto-potty and my poor little shlub had no interest. Well, one day he just said I want big boy underwear, I told him he had to go on the potty and that was it. Yes, there were accidents here and there but we were on our way. My point is, you will know when he's ready. Follow his lead and don't push. Also, he never used the training seat. I think kids want to go where their parents go. You can always try the little m&m treat after he goes trick. And there's always the aim at the cheerio in the toilet trick. But I promise you, when he's ready, truly ready, it will happen quickly.
Good luck!