Max came to us when he was 4 months old and was already 39 pounds. Even then he was a strong, determined boy. Now he's 14 months and 95 pounds. Technically, Max is still a "puppy" as far as mental maturity goes, but he is very much on his way to being a full-sized adult physically. Having your puppy trained early can help you and your puppy be able to successfully go places and do things that might be nearly impossible otherwise.
Max's mom, Lynn, is probably not much heavier than Max! Without his puppy training, she would likely not be able to walk him. She has done such an excellent job following up and practicing with him. While training an adult-sized German Shepherd isn't impossible, it is much more difficult to overcome bad habits, especially if the dog has fearfulness, anxiety or aggressive tendencies.