The old "dog years" formula (one year of a dog's life is equal to seven years of human life) never really worked for any dog, based on a comparison of the general lifespan of humans vs. dogs. Cats age at a more predictable rate than dogs do, mostly because we don't see the range of size and body types we do in dogs, but the 1-to-7 formula doesn't work for them either.How Old Is My Dog?
Consider two 10-year-old dogs, a Great Dane and a Chihuahua. Under the 1-equals-7 formula, they'd both be considered the equivalent of a 70-year-old person. And while that's probably not too far off the mark for the Great Dane (10 years for a Dane is indeed near the outer edge of life expectancy), the Chihuahua is likely still acting middle-aged.
But even the Great Dane didn't match the old formula when he was young. In the first year of his life, he would have attained most of his height, something no human 7-year-old ever does.
It's more accurate to think of the first year of a dog's life getting him just over the first big jump of adolescence, with the second year bringing him close to full adult maturity physically, although as in humans, mental maturity may still be on the horizon. From there, it really does depend on the kind of dog in question. I think it's more important to focus on the individual dog, with the knowledge that size and breeding matter when it comes to aging. Roughly put, you can consider your dog to be a senior citizen at 7 if he's that Great Dane, but not until 11-plus if he's the Chihuahua.
Your actions can influence your dog's aging process, by the way. In particular, dogs who spend their lives overweight or obese will experience chronic pain and illness earlier than active and healthy dogs of normal weight. So while you're taking precautions to keep yourself young, do the same for your dog, by watching his diet and encouraging him to get plenty of exercise.How Old Is My Cat?
What about cats? We all love easy answers, so after the idea of "dog years" became popular, we started seeing the same methodology applied to cats: Take the lifespan of a cat, compare it to a person, then get your formula, which is why you may frequently hear that 1 cat year equals 4 human years.
You're ahead of me already, I bet: A 1-year-old cat is far more mature than a 4-year-old child, and a 2-year-old cat is fully mature, which can never be said of a human 8-year-old.
Because cats have less size diversity than dogs do, however, in this case we actually can make the formula work, if we start calculating at a cat's second birthday. The first year takes a cat to late adolescence, and the second into young adulthood. You can then start counting in fours: Figure a 2-year-old cat at 24 "human years." and add four years for every one thereafter, making a 4-year-old cat the equivalent of a 32-year-old person. That makes a 9-year-old cat about 52 in human terms, and 16-year-old cat about 80.
But, as we love to say about ourselves, age is only a number. With cats and dogs (and people!), proactive, preventive wellness care with proper diet and exercise is the best way not only to achieve a longer life but also to have it be a happy, healthy one.