I have two boys and I remember the pediatrician telling me that there is no magic age when toilet training is appropriate but to make sure that when you begin really young like 18 months that you watch for cues from your son. If he is having TOO many accidents and both of you are becoming frustrated, then he may not be ready and you don't want him to feel constant failure. It was explained to me that it isn't always psychological or developmental readiness to toilet train but sometimes it is physiological. In other words, his bladder and brain may not be in sync with each other quite yet to even be able to control his urination. Everyone has differing opinions on when it is a good time to potty train. Our pediatrician who also worked closely with a child psychologist told us that it shouldn't take more than two weeks to toilet train my son (accidents will still occur periodiacally) but the majority of the time he should be trained. I know many people who have done it at 18 months and younger and succeeded very well, all I'm saying is make sure no matter what method you are using, take cues form your son.
Having said that, the most effective thing that I found was never to use pull ups because they are confusing, toys and treats are a great idea, and my kids needed to be kept naked in the house during toilet traing as much as I could. I know this sounds weird but with both of my boys, as long as they had underwear or pants on at all, they got lazy and went in them. If they were naked they went straight for the toilet. After a couple of days of this, they were pros! Good luck!