The puppy stage sets the inspiration for a dog's whole life. The size of this period can vary. For large or giant breed dogs, normally it takes about two years. For all other dogs, one year is generally the rule of thumb.
During this time period, puppies undergo rapid physical development including:
To put it in perspective, a human usually takes about 14 years to accomplish similar development – so that's a lot of growing for your puppy in a short timeframe!