I believe that training can and should start the actual day that your puppy comes home with you. Puppies are learning from the time that their eyes open and their little feet start working and they start exploring their environment (a lot of trainers and behaviourists call them little sponges). So since they’re learning anyway we might as well step in and teach them what we want them to know. Dogs are creatures of habit and routine. The question isn’t whether they will get into habits; the question is whose habits will they develop – the ones they come upon naturally, which are usually the things we don’t like, or the ones we teach them which are the things that make them great pets and companions?
A lot of breeders will actually start doing a little bit of training when the puppies are six and seven weeks old and some people if they’re lucky will get puppies who are almost house-trained at about eight or nine weeks, which is very rare, but it’s proof that they can learn that there are some places that are okay to go to the bathroom (meaning outside or on paper) and not other places (like your carpeting!)