You can get captive bred snakes from breeders as soon as they are established as good feeders. Could be as little as a couple of weeks old.

There are "breeders" out there that try and sell snakes fresh out of the egg that haven't even taken a meal yet and they should probably be avoided, but a breeder with a great reputation that cares about setting you up with a quality animal will do you right.

In my opinion, the younger the better ... that way you can grow with the snake and learn as you both go.

-adam