I started around 12 months with my daughter, though we stopped at 13 and then didn't start again till 15. I put her in trainers at 18mo, and now at 22 we are having a serious regression (had a new baby a month ago). But I am convinced she will be completely trained and done with regression nonsense in the next two months. Now some would tell you that I could have saved myself a lot of headaches by just waiting till she was two, doing a two day boot camp, etc. but all I know is that I am happy I did it early. I cloth diaper, and not having to wash her diapers has been great. In fact, I plan on starting training with my son when he is 6 months and/or able to sit up by himself.
A few things:
1. early potty training depends on timing and getting them to the pot. Kids need reminders until 2.5-3 years of age, as they get so wrapped up in playing that they ignore what their bodies are saying. In fact, my daughter is great about asking to be taken to the potty when we are not home, but when we are home, we have accidents, and I am convinced it's because she is too busy playing.
2. People will think you are crazy and tell you that he is much too young. Don't listen! Just because they need help, this doesn't mean they aren't ready. To me that's like saying they aren't ready for table food until they are over two because they can't use a fork and spoon correctly. There are many skills involved in learning how to use a potty,and the sooner you start teaching, the better, if you ask me.
3. The skills as I see them: (1) recognizing the difference between wet and dry, (2) recognizing the pressure/need to go, and (3) being able to get to the potty in time. With early training, they are dependent on you to get them to the potty, so your role, as I see it, is to teach them about 1 and 2 and not get frustrated until they are able to do 3 without you -- which may not be for over another year.
4. See the books someone else suggested. What worked well for us was the advice to read books and play in the bathroom every day. And model, model, model, and get everyone in your family, especially daddy, to take him with them when they use the bathroom.
5. Make the bathroom fun and don't get emotional. Become robo-mom, and hang in there. Early potty training can be frustrating, but it can also be rewarding if you can keep your cool and just understand that needing your help does not mean they aren't trained or trainable.