German Shepherd grows up in 40 seconds! In this video the person took pictures of the dog throughout the first year of his life and the person compiled the photos and created this cute video of showing the dog growing up from a pup to adult hood. It’s amazing how fast kids and dogs grow up. It’s almost like it’s a blink of an eye. I have read that a dog should be completely mature by two years of age. That’s amazing that they mature that fast. My hound dog is around five and it seems like she’s still a wild beast. She has so much energy no one can keep up with her.