Oh, that's so great!
Just be forewarned: a lot of the kids who start early get bored and quit with the potty along the way. Remember, it's a process, so don't be surprised if there's some backsliding.
We have pictures of my DS3 on the potty before he was 18mos, and it was all self-initiated. It just didn't take. He was trained in time for preschool, but just barely!
I still have to remind myself when he has an accident because he's too busy playing to stop and get to the bathroom: Process...process...process...
Hopefully this is NOT the case for you!
