I placed the potty chair in our bathroom when he was 18mths and he sometimes would sit on it for fun. A few days after he turned 2 he put up a fuss as I went to change his diaper so I sat him on the potty, he went. I took that as a sign and did the three day method & haven't looked back. I think it does depend on the child though, my friends 3.5 year just decided to train a few weeks ago.
SAHM, wife to K
and lucky mama to 2 boys! DS1 6.2010, DS2 4.2012
Living the simple life and loving it!