Caitlin has had a potty from about 6 months as the position and the routine of sitting on it after lunch every day helps with her pooping issues (or not pooping issues

).
She's an early walker too and also insists on being in the bathroom with you and laughs AT you when she sees you sitting on the "potty" then walks out again! Cheeky madam
Anyways, we were told by a specialist that just because she can associate the potty with what she should do in it doesn't mean her body is ready to poop/wee on command or for her to have any control over it.
I agree with GandT, it's pointless potty training the child if they can't get themselves undressed and ready to sit on it when they need to go. But it also doesn't hurt to introduce it at an early age so you don't have to deal with the fear of it when the time comes.
I'm going to have a read through the old TTing threads and get some ideas on when and how too