My friend's grandson had a potty chair from a very young age, but wasn't expected to use it. it was a gift, a well-made wooden one from a great aunt who passed away soon after his birth and gave his mom comfort in seeing it.
He wasn't really encouraged to use it, but obviously knew what to do as one night after his bath while daddy was putting away the tubs toys he sat on it and peed and pooped. He was 14 months old and Daddy thought it was a fluke.
The next morning he threw a fit when his diaper was being changed and they couldn't figure it out. While they were carrying him kicking and screaming to the kitchen for breakfast he struggled to get down. When he was put down to take off the tray from his highchair he ran to the bathroom, he wanted to use the potty! Seriously, the boy has been trained since 15 months, day and most nights, pee and poop, they think it has something to do with him wanting to be like his 6 year old brother.
You can put a potty in the bathroom, talk to your son about using the potty, let him see you going, and wait for him to be able to use it and be cooperative in doing so, more than likely at around 2 years of age.