A few years ago, I googled "Toilet Learning" and found a University of Michigan site for early childhood ed students. It gives the most comprehensive (yet, really very simple) way to assess a child's readiness. The window for toilet learning* (supporting the child to learn their body's cues that tell them when they need to use the toilet) is rather wide...and can go as late as 38+ months. Some will disagree, but with 18+ years experience of helping children and their families with this task, I have to say that it's easier if we start when the child is ready-- so you're on the right track.
My son wasn't ready until he was about 38 months old, and it's been so simple-- I think we've had all of 5 accidents since he started wearing underpants.:) The url of the article will say something like "angel units"-- I've used this info and had just the best results over anything else I've read. It will help you to see which area's he's ready in and if/where he needs more readiness or development. Best wishes!
*toilet learning is a newer approach to toilet learning which relies on the child's motivation and readiness.... it's a slightly different approach to the traditional stickers and candy potty training. This method is becoming used by more and more early childhood educators, because it respects the child's process and because it really works well for everyone. Not saying that potty training is bad, it's just that we have better research and understand how children learn so much better than we used to. :)