M.K.
We started when my daughter was a week or two shy of age 3. However, it wasn't exactly a conscience decision to wait...circumstances simply led to this. Once we started, there were no pull-ups and no training pants -- she went commando for one day. After day 1, regular panties from then on. She was trained, with no accidents in a total of 3 days. In retrospect, I think it might have helped that she was a bit older and had an understanding about what we were doing -- and could put her own effort into it. It worked for us. This did NOT work with my son!!! Girls are so different, aren't they!?!
(PS...we used pull-ups at night until her body was developed enough to wake her when she needed to go. This was about age 4 1/2 for her.)