When did you start potty-training?

Get your son on the potty and only put him in a diaper at night only. During the day keep him in big boy underwear, and ask him every 30-45 minutes if he has to go to the bathroom, and give him an incentive to go. After about 2-4 weeks take him off of the nightly diaper and only ask him if he has to go about every hour and a half. Soon enough he should be fully potty trained.