My mom had 8 of us, so she wanted us out of diapers ASAP. In her generation I think it was more common to train early anyway. She would have been 92 this year. So my philosphy followed my moms. DS was potty trained the summer before he turned 2 in September. DD was much different. One day DD was running around, 'air-drying', and a fresh diaper was lying on the couch. She suddenly stopped, ran over to the couch, put the diaper between her legs and pee'd on it. She was 16 months old. I thought, 'hunh, might as well get the potty chair out'. I put it out, explained it was hers, and she was trained. Within a month she never even had an accident again. Her own 2nd daughter had some real potty issues though. The best advice I could give her was, "How many kindergartners go to school in diapers? Just back off on that one and she'll start using the potty eventually." And she did, and is in K, completely potty trained.
Different cultures have very different ideas though. I had a co-worker from India. She's older than I. Babies were trained by a few months old there. It might be more accurate to say the moms were trained to signals the baby gave, but the babies used a potty.