We've all heard that a dog ages seven years to each human year. The old seven dog years = one human year is a loose guideline, with some caveats. For one thing, a year-old human child is usually walking, talking and wreaking havoc. A Chihuahua is pretty much an adult at that same one year of age. But a year-old Mastiff or Newfie is usually still a big, awkward puppy.Smaller dogs often live longer than larger breeds. Pebbles, a Toy Fox Terrier, is the documented oldest living dog at 22. Bluey, a heeler in Australia, lived to be 29!