It depends on what you mean by "started".
We got the little potty, started reading her potty training storybooks, and started talking about where mommy and daddy go peepee and poop at about 13 months.
She wasn't willing to sit on the potty until 27 months. Before that, she'd jump up and run away the instant I put her on the potty. If I tried to hold her there, she'd scream.
Once we truly started at 27 months, she was daytime trained within a month.
Remember that nighttime dryness has nothing to do with potty training. A fully potty trained child may wet the bed until 7 (or even later).
You'll have the most luck if you work WITH your child instead of trying to force your child to some "you are old enough" or "I am sick of diapers" schedule.
at 11:43 AM on Feb. 24, 2009