It's not age based.
There are two schools of thought:
(1) Start anytime, even right after birth. You will actually be training YOU. You will learn to know when to take your child to the potty. You will take them, work the clothes, etc. You will save on diapers but spend lots of time and energy. You can also "brag" to people that you have started training.
(2) Wait until the child is ready. Then you start out by taking the child on a schedule until they learn to tell you they need to go... that can happen quickly or take months. The child is usually able to work his own clothes, get on and off the potty, etc by himself. You will use more diapers but training will be much quicker. If you read him a potty training storybook now and then, you can still tell nosy relatives that you have "started".
at 11:15 PM on Jan. 20, 2009