Here's one of several sites that gives some great "readiness" checklists. I wonder whether your little guy is truly ready for success yet: http://www.parentingscience.com/toilet-training-readiness...
Kids who are started earlier generally "train" for however long it would have taken them to be physically, emotionally, and cognitively ready for success. A child who reaches that stage at 29 months, for instance, will finally succeed at 29 months, whether he was started a week or a year earlier.
It's great that he's doing well and that you're keeping it positive. Can't beat that! But not all younger children will be able to achieve positive results at an early age, and setting up an expectation that they should can actually set the process back and leave kids with a sense of failure or resistance. And not all parents will have the attention or availability to use the "set the timer and direct the child" approach, or the "be attuned to your child's signals" approach. Families who allow the child to lead will still end up with fully trained children just as soon as the child is mature enough. For many kids, that will happen somewhere between 2.5 and 4.5, with boys tending toward the later age.
Parents who are truly dedicated to getting their kids to a potty every time can and do get children who are trained much younger (with ongoing parental attention). Those children are sometimes, but not always, emotionally committed to ongoing success. The obligation just looks too large or onerous or pointless for many kids, so backsliding after a period of apparent success is common. Can those kids be cajoled or maneuvered or punished or bribed into ongoing performance? Sometimes, but that doesn't seem to be the same thing as successfully achieving that developmental milestone, which can become totally voluntary only when the child is both physically and emotionally prepared for it.