It's not age related.
You can start anytime or you can wait until your child seems really ready. Sometimes you can't really tell if a child is ready or not until after you've started. If they resist, back off. If they happily try to learn, keep going.
Remember - it has nothing to do with age, nothing to do with intelligence, a child doesn't have to be able to speak or work his clothes -that it helps, and a child doesn't have to hate wet or dirty diapers - though that helps too.
The main thing to look for - can your child go about 2 hours between wet diapers or does he wake up from his naps dry? Waking up from overnight dry is not required... just a couple of hours, not 12, means he is learning to control his bladder.
at 5:42 PM on Apr. 24, 2009