There is no best age to train them. It's sort of like asking "What's the best age to force him to feed himself".
You can start anytime you want. Some pick a milestone birthday like 18, 24, or 30 months. Some go by the readiness signs the child gives. Some have a deadline like starting preschool.
The more readiness signs - regardless of age - that your child shows, the quicker he will learn. The few signs, the longer and more frustrating training will be. Some kids are ready at 18 months and learn quickly, becoming accident free in a couple weeks. Some aren't ready at 30 months and have accidnets for months. It has VERY little to do with any method you choose or any magic parenting skills.
How to start?
Take him to the potty every 45 to 60 mintues until he starts to get it. Then switch to every 2 hours. Then switch to just watching for the potty dance.
at 11:53 PM on Mar. 20, 2009