In my experience, it is unusual to be allowed to take home a puppy of less than 8 weeks of age, and certainly not less than 6 weeks. In this respect it is never too early to start but a great deal of patience and understanding will be required. You can do a lot to train your dog without even knowing it. If she begins to go to the toilet pick her up and carry her out to where you want her to go, and then reward her. By this means, she can learn a great deal by association and should soon begin to try and get there herself by about 8-10 weeks.