It depends on the dog. I have a beagle who is 12 and acts like a puppy still. He has so much energy and is still so playful. The vet asked us if we had his birthday right. We got him at 2 1/2 and he was clearly full grown and we got him from a breeder my grandfather knows. His papers say his birthday as well. He just happens to be healthy and happy and extremely energetic.
