“If I miss too many gym days, I can really feel it — a stiffness creeping in here and there. And if I let that set in, well, God help me,” he said.

Dick Van Dyke is looking back on his extraordinary life and legendary career.

The 99-year-old actor shared how much his daily life has changed as he approaches his 100th birthday on December 13 — along with the realities of aging — in an essay published in The Times on November 13.

“It’s frustrating to feel diminished in the world, physically and socially,” the Mary Poppins star admitted. “I still get invitations to events or offers for gigs in New York or Chicago, but traveling takes so much out of me that I have to say no. Most of my visiting with people has to happen right here in my home.”

He described some of the “physical deterioration” he has experienced in recent years, comparing it to the older characters he once portrayed on screen.

“Like those old characters, I’m now a stooper, a shuffler, and a teeterer. My feet give me trouble, and I lie down as often as good manners will allow,” Van Dyke wrote. “Those fake old-timers smacked their dentures. I chew nicotine gum all day long — even decades after quitting smoking! My eyesight is so poor now that origami is out of the question.”

He noted other challenges too — difficulty following group conversations, frustration with his hearing aids, and even the simple act of eating meals.

“At mealtime I spill things, and when my wife Arlene [Silver] asks me to put on a clean shirt before we go out, I get impatient. ‘It’s got blueberry all over it,’ she’ll say. And I’ll answer, ‘Polka dots are in again!’”

Still, the Dick Van Dyke Show icon refuses to let these obstacles stop him from staying healthy. He revealed that he continues to go to the gym three times a week.

“I don’t know why this is something I still want to do, but it is,” he confessed. “If I miss too many gym days, I really can feel it — that stiffness sneaking up on me. If I let that set in, well, God help me.”

To keep himself motivated, he sets little “carrots” to look forward to — like “a huge smoothie or a frothy caffeine treat” after a workout, or even a “well-earned nap.” The gym also gives him deeper rewards: “a sense of accomplishment to enjoy,” a sharper mind, and what he describes as “a full-body tingly exhilaration.”

He also shared details of his workout routine, which involves moving through a full circuit of gym machines without stopping.

“I start with the sit-up machine. Arlene says I could do 500, but that might be an exaggeration. Then I go through all the leg machines faithfully — my legs are two of my most cherished possessions. Then it’s on to the upper body.”

Music, he said, is the secret to keeping him going. He hums, sings, and even dances his way from one machine to the next.

“You heard me — dancing! And if I’m really feeling it, I’m not a quiet hummer; I’m a full Broadway belter.”

By the time he finishes, he says he’s “in a sweaty rush, blood pumping from fingertips to toes, and my spirits soaring.” And every time he leaves the gym, he asks himself with excitement, “OK, today — what’s next?!”