On the cusp of his 90th birthday, Dick Van Dyke still dances pretty much every day. While the elastic-legged “Mary Poppins” actor may no longer be able to tap and twirl with a waddle of animated penguins at his heels, he has been known to swivel his hips through the supermarket. “I think I should do a series,” he says: “Dancing in Stores.”

As the title of his new book, “Keep Moving” (Weinstein, $25.99) suggests, Van Dyke believes staying active is key to staying alive. Good genes help, too, he confesses; his mother lived till she was 96.

“I want older people to realize a little exercise is better than none,” he said. “Even just 10 minutes. I’m trying to talk people out of throwing in the towel.”

Van Dyke practices what he preaches. His typical day begins at 6 am, with a cup of coffee and a trip to the gym for a light workout that includes the treadmill and weights. He’s never used a trainer; he says he understands his body better than anyone else. Van Dyke’s activity level is especially amazing given that he was told he had arthritis at 42, in the midst of the filming of “Chitty Chitty Bang Bang.” That diagnosis emboldened him: “I’m not going to stop dancing, no matter what,” he recalls telling himself.

Even at home in Malibu, Van Dyke says, “I can’t sit still.” He trots around the house, he says, “Edith Bunker-style.” (A recent video for the country band Dustbowl Revival shows Van Dyke gliding through his home in elegant movements reminiscent of Fred Astaire.)

Van Dyke, who still performs with his quartet Dick Van Dyke & The Vantastix, says there are three keys to a long life: “You need something to do, someone to love and something to hope for. I had all those — and more.”

He also had his share of vices (two to three packs of cigarettes a day, five or six post-work drinks), though he quit both smoking and drinking years ago. He says giving up cigarettes, “the worst of all addictions,” was much harder.

In recent years, he has also suffered from pneumonia and a collapsed lung. “Then I got right back exercising,” he says. “I feel fine now.”

Much of his good health –- and cheer — he attributes to his wife, Arlene Silver, a former make-up artist and a dancer, who is 44.

“She changed my life,” says Van Dyke, who outlived his first wife, Marjorie Willett, and his long-time companion, Michelle Triola, who died in 2009. Later, when “word got out I was dating,” he writes in his book, “my popularity skyrocketed. One woman waited for me every morning in my local coffee shop. She was like a well-intentioned stalker with a nice wardrobe. My phone rang constantly.”

At 89, does Van Dyke feel old? Not exactly. “At 80 I remember thinking, ‘This is perfectly acceptable.’ But in the last decade I have had issues with my hands: I like to play the harpsichord, and I can’t reach the full octave. And I have difficulty with my short-term memory –- though I think that started in my 40s.” (In his book, Van Dyke thanks his neighbors for the many times they have returned his lost wallet to him.)

A former avid tennis player and sailor, Van Dyke says he can no longer do either, the latter because of a problem with his inner ear that he developed in his 80s. “I miss the ocean,” he says. He still does his famous doodles and enjoys doing 3-D computer animation as a hobby. He also spends time with his old friends Carl Reiner (93), Mel Brooks (89) and Norman Lear (93). “When I see them, we have to talk about the past,” he says.

Van Dyke’s newest project involves the restoration of his childhood home, in Danville, Ill. The once abandoned house is to be made into a museum and a center for the “Dandy Vandy” Dick Van Dyke Foundation, a nationwide effort to inspire young performers.

Van Dyke doesn’t have much of an appetite for current pop culture, sitcoms or music, save for Adele and Amy Winehouse, who he says reminds him of Billie Holiday and Ella Fitzgerald. His favorite song, perhaps not surprisingly, is “Jolly Holiday.” “I sing it every day. It’s an ode to morning.” When singing, he says, it’s impossible to feel blue.

Bad moods seem rarely to strike Van Dyke anyway, even as he comes closer to the end of his life. “I know death is coming, and it’s a terminal condition, but for some reason I don’t worry about that. The act of dying — if painful — I would fear. I want to go when I’m dancing on the stage.”

But before that –- long before, one hopes — he has his 90th birthday to enjoy, in December. To commemorate, he says. “I’m going to Disneyland, to my homeland. Some friends and I will have dinner and maybe go on some rides.”

It seems a fitting way to celebrate for a man who finishes every day with a big bowl of vanilla ice cream with chocolate sauce. A spoonful of sugar really does help the medicine go down, he says. “It’s very, very true.”

A few more bits of Van Dyke wisdom for young and old:

On feeling young: “I am a child in search of his inner adult,” he writes in his book. “Scripture says you should put aside childish things when you grow up. I take that to mean willfulness, self-centeredness, and things like that -– not imagination and joyful curiosity.”

On staying sharp: “I learn something new every day, like lines from Shakespeare,” he writes. “I started with ‘King Lear’ and enjoyed the sounds of my recitations as much as I did the accomplishment of having committed them to memory. The language is beautiful and the writing is full of truth: ‘Love is not love when it is mingled with regards that stand aloof from the entire point.’”

On love: “You are never too old for romance. A candlelight dinner, a slow dance, a stroll under the stars – these are as potent and magical at eighty-five as they were at twenty-five,” he writes.

His advice for young people: “I hope kids will try to make their marriages work,” he says. “The romantic notion of love is fine –- but unless you are good friends it won’t work.”

On how we treat old people: “We used to venerate old people, and now they’re just ignored and sometimes warehoused,” he says. “I want to start a Gray Revolution.”

The secret to a good night’s sleep: “Forgiveness is the best sleeping pill,” he writes.

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