I read that in the 50s the average age to potty train was between 15-18 months whereas now it's 3.5 years!! 
DD is 16 months and showing awareness of bowel movements, e.g. pointing at her nappy and saying "po po" (although not consistently) and taking herself off to a corner to do her business.
So we thought it would be good to at least start the process of getting her used to potties by having them in the house for her to get used to seeing. Although that's as far as we've got so far... But hey, it's a start!
Anyone else started potty training at a similarly young age?