When you adopt a dog, sometimes even your veterinarian can’t really conclusively tell you how old the dog actually is. With puppies, you can get a good idea of their age by looking at their teeth. Puppy baby teeth are replaced with adult teeth by 6 months old. After that, vets usually look at the amount of tartar and tooth wear to estimate a dog’s age. Unfortunately, tartar can depend on food and even the environment the dog was exposed to as a youngster. Like people, some dogs just have really bad teeth, so determining their age can be a challenge.
The old adage about each year of a dog’s age being equal to seven human years isn’t really true. For example, a one-year-old dog is roughly like a 12-year-old kid. A two-year-old dog corresponds to a 22-year-old human. Anyone who has ever owned a dog would have to agree that canine adolescence can range anywhere from about 7 or 8 months to 2 or 3 years old. Dogs reach middle age around 6, which is equivalent to a 45-year-old human. At 10, she’s like a 65 year old; at 13 an 80 year old; and at 15 like a 90 year old.
A few obvious signs indicate that your dog is a senior citizen. Depending on the breed of dog, you may notice that her muzzle starts to go gray. Of course if you have a white dog, you won’t see that clue. And some dogs actually go prematurely gray, just like humans do.
Many older dogs also get a type of cloudiness in their eyes. This condition is a hardening of the lens protein and is not the same thing as cataracts. Although it may look somewhat like cataracts, the dog can still see. However, if you notice that your dog’s eyes look cloudy, you should check with your veterinarian.
In general, it’s a good idea to keep a close eye on your canine friend as she ages. Some illnesses become more likely as dogs age. Often many of these diseases can be treated, which can improve your dog’s quality of life in her senior years.
Some dogs do live a lot longer than others. No one knows how long a particular dog will live, but certain genetic predisposition to disease may shorten a dog’s life span. For example, many Cavalier King Charles spaniels have a genetic problem with mitral valve disease, so they often don’t live as long as other medium sized dogs.
In general, the life span of a dog goes up as the size goes down. Giant breeds like Great Danes age faster than Chihuahuas. Because giant breeds live 7-10 years, they actually are considered "geriatric" starting as early as 4 years old. Conversely, small breeds can live up to 18 years.
If you have a mutt, you can guess her lifespan by considering the approximate breed makeup and size. But no matter how long your "best friend" lives, it probably won’t be long enough.