L.F.
That's the magic question. There is no right age to start. The answer is start when your child is ready. My daughter showed interest in the potty at 18 months, but wasn't actually trained until about 6 weeks before her third birthday. It wasn't until we quit trying so hard to get her trained that it just clicked with her. My 4 year old son was day trained right after he turned 3. We took it real easy with him. He got night trained when he was 3 1/2. We've just started putting our 2 1/2 year old son in underware (at his request) and it's going okay so far. Let the child take the lead.