Some things you learn in life and think "this is gold". This is something I learned. And now friend, I share with you.
A little book that is called: "Toilet Training In Less Than A Day" By Nathan H. Azrin, PhD and Richard M Foxx, PhD and it's legit.
Yes, it's a bit 1970's but the principles of behaviour training and child psychology don't change that quickly. I'll give you the quick gist of the book here and encourage you to look for it (not easy to find but I have had two second hand copies from Amazon at about $5 each).
Age and Stage: The book covers research on toilet training and reports that children at age 20 months are ready for toilet training (except those with developmental delays). Of course there might be individual variance of a few months either side. It gives you an easy guide to look at physical readiness, behavioural readiness and language readiness.
Prep: The book is a complete how-to guide for toilet training. The reason it can provide a fast learning approach is because it uses research proven methods of learning. This means that you model (show your child what to do with a doll), praise, praise, praise and provide rewards, which positively 'shapes' behaviour.
PS: Did I mention it's a quick skim read and straight to the point?