This is a sad question to answer but I will be brief and say it depends on the breed of dog you are regarding.
Explanation:
The average life expectancy for dog is normally 10-13 years, much shorter than the human lifespan. Sometimes there are outliers, some can live to 20 in rare cases of dog's life's can be cut short due to mistreatment, accidents, or genetic makeup. In any case if you are looking for a dog and want one that lives a long time try to find a Maltese of Australian Shepard for adoption. They live to be 12-15 years old.
