It always amazes me how long pet cats can live. I’ve known a handful of people who have had cats live to be 17, 18, even 20 years old.

So I wondered: Is this normal?

As a general rule of thumb, Janet Tobiassen Crosby, DVM, who addresses this veterinary medicine issue at about.com, says a cat who is 10 years or older should be considered middle- to senior-aged. And the American Society for the Prevention of Cruelty to Animals says the average lifespan of an indoor cat is 13 to 17 years.

So yes, it’s fairly normal for cats to live a long time. (You’ve heard of cats’ nine lives, right?)

My Google-fest led me to other sites that provided some “oldest cat trivia,” including these tidbits:

n In July 2010, the St. Pete Times wrote about Possum, a 28-year-old cat who lived with her human in Holiday. Possum was the 2010 Cat Fancy winner for America’s oldest cat.

n Susan Logan, editor of Cat Fancy, said in that article that the oldest cat from reader submissions came in 2007, with 36-year-old Baby.

n The oldest cat ever, according to Guinness World Records, was Creme Puff, who was born Aug. 3, 1967, and lived until Aug. 6, 2005 -- an amazing 38 years and three days. Creme Puff lived with her human, Jake Perry, in Austin, Texas.

I’m not sure you would really want a 38-year-old cat, but Wendy Diamond, “Today” show pet lifestyle contributor and Animal Fair editor-in-chief, has some tips to help cats live a longer life and keep a senior cat feeling younger.

n Assess your cat’s age.

You know those quizzes on Facebook -- "What’s your real age? -- that are supposed to determine how old you are despite what the calendar says? Well, cats have one, too.

Diamond has partnered with Hill’s Science Diet to launch the Science Diet CatAge Quiz. By answering a handful of simple questions, you can determine your cat’s real age and then focus on what he or she needs to keep feeling frisky. You can take the quiz at HillsPet.com/DefyAge.

n A healthy body is nothing without a healthy mind to match.

Cats and dogs can suffer some cognitive difficulties later in life the same as people can.

Diamond reminds us that older cats may become bored or disinterested in activity, so it’s important to keep their minds active and engaged to stave off the trappings of old age like senility or depression.

Now, cats aren’t the best at crossword puzzles and Sudoku, so perhaps a problem-solving toy is the answer. In the last column I mentioned Ella’s “kibble Kong,” which keeps her busy and entertained while I’m at work. Something like that might be a good idea for a cat, too.

n Good skin care.

You might not be able to see a cat’s wrinkles, but I’ll bet they’ve got them. And just like with people, those wrinkles come from the loss of natural oils. In cats, these oils promote healthy skin and fur and benefit skin elasticity. This in turn helps build their protection against cuts and scratches.

n Cats are what they eat.

There’s an old saying, “you are what you eat,” and there’s the computer-age saying, “garbage in, garbage out.” Both apply to animals. A healthy diet will go a long way to keeping your pet healthy.

Diamond points out that older cats have delicate digestive systems and benefit from a good senior cat food. Most of these contain antioxidants and omega 6 fatty acids, fish oil for healthy brain function, and glucosamine and/or chondroitin for healthy joints. Also, look for a formula that’s in small kibble so it’s easier to chew and digest.

n Visit your vet.

When my Reba turned 11, I started taking her for checkups every six months. Her vet, Dr. Mike Mossler at Bayshore Animal Hospital, said that was a good idea because problems can spring up in older animals that would be much easier to treat if caught early. The same is true for cats.

Sometimes animals start doing things they never did when they were younger and we tend to chalk it up to, “well, they’re getting older.” Maybe, maybe not. It doesn’t hurt to consult a medical professional when your cat acts odd. Never assume strange behavior is just aging.

n Increase agility.

It’s a rare cat indeed who walks on a leash, so to keep tabby from getting flabby it helps to make it easier for the older cat to get around. Ramps or footstools leading to your pet’s favorite places will keep them from the stress of jumping too high, up OR down.

Reba was stubborn about using a footstool to get on the bed, but after I forced her to use it a few times by blocking off any other access, she decided it did help and now she uses it all the time. So instead of just giving up and laying on the floor, she still gets some exercise by jumping on the footstool (a small foot locker, actually) and then on the bed.

Another one of Diamond’s suggestions is to treat your pet to a daily massage. It can help stimulate healthy muscles and leave them more agile and amiable. And who doesn’t want that from their cat?

M.K. Means, Herald copy editor, can be reached at 745-7054.