I can't speak for myself as i've only just started with my DD1 who is 2.8yrs old and well lets just say, i think i might be in for the long haul!! - But my sister who has 3 boys and 1 girl said and all her boys weren't TT until about 3.5yrs (day/night) whereas her DD was trained day/night by 2.3yrs, so maybe it is true? either that or her DD watched all her big brothers doing it and didn't want to be left out

sorry, i'm not really much help but just thought I'd share