This video has veterinarian, Ian Dunbar, discussing how a puppy at eight weeks of age should be ready for it's new home. He says by eight weeks it should be potty trained, but I have a hard time believing that. I have never tried to house train a puppy before eight weeks, but I guess it could be possible.
With punishment training they always said you had to wait until they were six months old so you didn't hurt them. Now with positive reinforcement training, that seems like a long amount of valuable time wasted. In just a few weeks I have taught Amelia what some dogs only learn in a lifetime.