Charts, such as this, have been established that put dogs’ and cats’ aging on a non-linear scale in proportion to human life expectancy. By “non-linear” we mean that there is not a straightforward “7 years for 1 year” relationship. For example, a three-year-old cat (or a dog under 20#) already have a human longevity equivalence of 22-28 years, meaning the first years of maturation of dogs and cats are very accelerated.
Another factor is the size of the pet. Small pets age more slowly and live longer than large breeds. To further illustrate this relationship, the three-year-old dog over 120 pounds is already 39 years old, an increase of 26% in rate of aging.
Broadly speaking, many small-breed dogs can be expected to live to be 15-18 years of age. Giant breeds such as mastiffs and Great Danes may be truly geriatric by only age six and infirmed soon after. Giant-breed individuals over 10 years of age are truly rare.
It is difficult to overcome one’s longevity genes, whether canine, feline or human. Still, TLC counts for a lot. Proper diet, exercise and rest are crucial regardless of one’s species. The importance of regular medical care at your pet’s doctor cannot be overstated. This includes annual or semiannual physical examinations, vaccinations on schedule and heartworm preventive given every month year-round.