Actually, in many countries, they start training the babies as early as three months. Mom will hold the baby between her legs and let him go in the potty or the pot (depending on where they are). I've also heard that if you make the noise (sssss or grunting) it will clue the child to make those noises when the urge strikes.

I think its not so much that the child is trained as it is that mom is trained. However, anything is possible.