Why Do Dogs Age So Fast? The Answer May Surprise You! (2024)

An older dog with a brindle coat resting with his head down on the floor.

Dogs go from being adorable, bouncing puppies to adult dogs showing signs of growing old in an unbelievably short time frame.

From chewing slippers to struggling with stairs. From zipping around the yard to sleeping away the day. From endless energy to slower movements and graying muzzles.

It’s heartbreaking to watch and is a constant reminder that every day should be treasured, but why does it happen so quickly?  

Why do dogs age so fast? Dogs’ rate of aging and lifespan are predetermined by their genetic makeup. There is rapid aging during the first year of life, which sets the stage for a short lifespan. Their high metabolism speed is also believed to accelerate the aging process. 

Aging is inevitable, and some species, like our canine companions, age at an alarming rate.

In the following, we’ll not only explore why our dogs age quickly, but we’ll also look at the phenomenon of big dogs aging faster than small dogs and what you can do to give your dog the best chance at a long and happy life.

Why Dogs Age So Fast

Aging, or senescence, can be defined as, according to NCBI, “the time-related deterioration of the physiological functions necessary for survival and fertility.” 

In the first year of a dog’s life, there is rapid growth and development. That first year of a dog’s life is roughly equal to the first 15 years of human life.

The second year of a dog’s life is equivalent to about nine human years, and each following year is about the same as four human years, according to AKC.

You can see that from the moment a puppy is born, he begins to age quickly, and, as with people, the canine body slowly deteriorates over time.

Although more studies need to be done before we’ll fully understand why dogs age so fast, we do have a general idea of the influencing factors, which we’ll examine below.

Genetic Makeup

You wouldn’t expect a bat to outlive an eagle or a tiny bug to live longer than a monkey, right?

Maybe you’ve never paused to consider that we tend to associate size with longevity and rightly so.

Some of the longest-living creatures are huge, and many of those with short lifespans are quite small. Consider this:

Animal Average Size (in pounds) Lifespan (in years)
Bowhead whale 120,000  Close to 200 
African elephant 14,000  Up to 70 
Grizzly bear 800  25-30 
Human 100-200  70-85 
Dog 20-80 10-15
Cat 9 12-15
Mouse .5-1 ounce 1-2

Generally speaking, the larger the creature, the longer the lifespan. There are, of course, a few exceptions, but the basic assumption holds true.

Every species is held captive, in terms of lifespan, by its genetic coding passed down through generations.

Granted the numbers may fluctuate somewhat due to environmental factors, dietary changes, or other determinants, but they don’t change rapidly or without cause. 

Dogs, just like all other species, can only live as long as their genes dictate.

Faster Metabolism Rates

One theory in regards to dogs’ rate of aging revolves around metabolism, the chemical processes that occur within the body.

Typically, the larger the animal, the slower the metabolic rate and vice versa.

Because dogs are fairly small, their metabolic rate is rather high, which results in the formation of more free radicals and a faster rate of cell and tissue deterioration.

Basically, their bodies must work harder to function, and they wear down faster as a result.

Why Do Large Breeds Have a Shorter Lifespan Than Small Breeds?

Here, we’re treading into murky waters. The reason behind smaller breeds outliving larger breeds (often by more than three times) is not yet fully understood.

Large animals generally live a lot longer than smaller species, but in the case of breeds within the dog species, the opposite is true – large breeds have a shorter lifespan than small breeds.

Likely, growth hormones play a significant role in the reduction of lifespan.

You see, although large and small breeds both reach full size in roughly the same time frame (12-18 months), large breeds grow a lot more within that time than small breeds do.

It’s assumed, though not yet proven, that this rapid growth contributes to accelerated aging and consequently a shorter life expectancy.

It’s interesting to note that this study determined that large breeds tend to have a higher rate of inbreeding within their lines, which negatively impacts lifespan.

This also explains why mixed-breed dogs tend to live longer on average than purebreds.

How To Help Your Dog Enjoy a Long, Happy Life

An old black-and-white dog running in the grass with an orange ball in his mouth.

While it’s disheartening to consider how relatively short your dog’s lifespan is compared to ours, there are simple steps you can take to make sure that every one of your dog’s days is enjoyed to the fullest and you’re giving him the best chance of living the longest life possible.


Feeding your dog a high-quality diet from day one is one of the most important things you can do.

There are, of course, complete-nutrition kibble diets, but some are better than others.

Be sure to check with our Ultimate Guide to Food and Treats to learn what to look for and what to avoid.

Feeding raw or homemade diets is also an option and perhaps a better choice for fostering longevity, but be sure to consult with your vet or a canine nutritionist to be certain that your dog’s daily caloric and nutrient needs will be met.


Exercise is important for every stage of your dog’s life, perhaps even more so as aging fights to slow him down.

Regular activity will help keep your dog mobile for longer, will help prevent obesity (a leading cause of early death), and will release endorphins – those feel-good hormones.

Additionally, exercise has been shown to:

  • Combat muscle loss and deterioration.
  • Improve circulation.
  • Reduce stress levels.
  • Engage the mind.
  • Help reduce pain and inflammation.

Just be aware of your dog’s limitations, and consult with your vet before beginning any new exercise regimen with an older dog.

Quality Time

You are the center of your dog’s world. It stands to reason that the more quality time you spend with your four-legged buddy, the happier and more fulfilled he’ll be.

Make it a point not to simply exist in this same home with your dog but to actively participate in activities with him each day.

This could be as simple as going for a walk together, playing fetch outside, giving him a good brushing and a belly rub… you get the idea.

Whatever your dog enjoys doing, make sure it happens frequently so that he’ll always have something to look forward to and live for.

Routine Veterinary Care

Regular checkups can identify and rectify many potentially life-threatening conditions before they progress past the point of treatment.

Your vet can advise you on dietary changes and exercise as your dog advances in age.

Dental health is also very important as it has been shown to affect longevity. 

A Quick Look Back

Rapid development early in life, genetic determinants, and fast metabolism are all thought to be behind the fast rate at which dogs age, and this also means that their lifespans are much shorter than ours.

Rest assured that your dog is not spending his days dwelling on this, and neither should you.

One of the things we most admire about our furry friends is their ability to live life in the moment. There is definitely a lesson to be learned there. 

Embrace each day with your dog as a gift, and focus on the present.