A dog year is actually only about 7 years old. In other words, one human year is equivalent to seven "dog years." This myth likely started because dogs age more rapidly than humans in their first two years of life. For example, a one-year-old dog is roughly the same age as a 15-year-old human. But after that initial period, dogs age more slowly than humans. By the time a dog reaches the age of 9, he or she is approximately the same age as a 45-year-old human. So, while a "dog year" may be shorter than a human year, it's not nearly as short as you might think!