Puppies are said to grow from the outside in. This means that the body parts on the outside – paws, tail and ears – grow to their adult size first. Think back to when your pup was 12 to 16 weeks old. He may have had adult, or near adult-sized, paws which likely seemed out of proportion with the rest of him. His ears and tail would have been the same – they sometimes grow to a startling length at an early age, and it can take a year or more for your pup to "grow into" himself.
Is he there yet?
How will you know when your puppy is no longer a puppy? He'll start filling out. His chest will get larger and he'll put on some pounds. He may get a bit longer and broader. His head will fill in and he'll stop looking like he's all legs and start looking more in proportion. His back will appear more level, instead of sometimes looking taller in the rear than in the front.
From a behavioral point of view, his wild racing around the house may all but disappear. He'll calm down a bit – in proportion to his breed and who he is. Some pups calm down so much people worry they might be ill. Others continue on, energized and bounding, into adulthood and beyond.
It's an astonishingly fast metamorphosis and once it's done, you'll look back at those puppy pictures and wonder, "Was he ever really that small?" Although puppyhood can be trying at times, and although you have much to look forward to with your adult dog, most puppy owners feel a bit nostalgic for the time when their dog was still a puppy.