William Robinson may be 91 years old, but he's uncommonly active. His gait and demeanor are energetic. His twinkling blue eyes are clear and attentive. In conversation, he's sharp. One could easily mistake him for someone decades younger.

What are his secrets?

One key ingredient is exercise.

"Exercise has always been part of my life and it always will be," Robinson said as we sat under the hau arbor between the Fort DeRussy outdoor racquetball courts and the beach. This is known as his "turf," and everyone there greets him warmly. They all call him "The Commander."

Since the 1950s, Robinson has been a fixture at the outdoor courts. He has played racquetball here with all eight of his children and his wife of 55 years, Joan. He has also played with many of Hawai'i's top racquetball players and professionals, as well as Wilt Chamberlain and Tom Selleck.

Robinson's first sport was skiing. Growing up in New Hampshire and Vermont, he couldn't get enough of the snowy slopes. He swam all his life, until about 10 years ago. He played volleyball until the cement floors started to affect his knees, when he switched to racquetball. He quit racquetball fairly recently, not because of problems with bones and joints, but because macular degeneration affected his vision. "I was afraid I might hurt someone," he said, in a half-joking way.

Now he runs (yes, runs) on the beach at Fort DeRussy, between watching his multitude of friends play outdoor racquetball and whipping them at chess.

"The man is like the Eveready bunny," friend and fellow racquetball enthusiast Rod Felton said. "He just keeps on coming down to the beach every day to work out, at 91!"

IT'S NOT HIS GENES

Robinson insists his health and longevity are not genetic. Everyone in his family died at an early age, his brother at just 50. "Whatever I did, I did it on my own," he said.

Another of his secrets is that he eats slowly. "I do it consciously and I'm always the last to leave the table," Robinson said. He puts his fork down often between bites and chews thoroughly.

His diet sounds like a nutritionist's dream. No salt or sugar appear on his table. His breakfast usually consists of fresh fruit, juice and cereal or an English muffin or two. Lunch is a salad, sandwich or soup. Dinner is fish or chicken (seldom red meat), a salad and vegetables. It takes him an hour to eat a meal.

And Robinson eats only one item on his plate at a time. For example, he'll eat all of his chicken, then all of vegetables, then all of his potatoes. "By separating each item, I find I eat more slowly," he notes.

He drinks a glass of wine each evening and enjoys an occasional beer.

Chocolate is a passion. Robinson eats a little dark chocolate every day; Dove is his favorite.

ALL ABOUT BALANCE

While Robinson is an extremely active 91-year-old, getting up early to trade on the stock market and track his investments, driving himself to DeRussy every day, gardening and doing woodwork, he also values his sleep. He sleeps around six or seven hours a night and takes an afternoon nap every day for an hour.

He takes a multivitamin daily, as well as supplemental vitamins C and E.

Robinson feels strongly that the key to having a long, healthy and happy life is having a purpose.

"My life has always been one of building," he explained. He has built seven homes in Hawai'i. He recently sold his Makaha home, which had both volleyball and racquetball courts. He now lives in Nu'uanu Valley, where he has created an award-winning garden, and a pond fed by Nu'uanu stream.

After retiring from the Navy, Robinson started two small businesses: WW Distributors, which imported souvenirs, and the restaurant Windows of Hawai'i.

Pete Britos, an avid racquetball player who is tournament director of the Black Sand World Championships, has known and respected The Commander for more than 25 years. "I was always grateful and amazed at how gracious and encouraging he was — and he didn't even know me," Britos said. "I was just some local kid from the North Shore who would come down and try and beat everyone who got in my way, including him."

Britos says The Commander is a continuing source of inspiration, for his "fortitude, positive spirit and can-do attitude."

Why is this retired rear admiral called The Commander? Robinson explained that when he first started playing racquetball at Ft. DeRussy, everyone assumed he was in the Army, since DeRussy is an Army base. So they called him "Colonel."

"Since I was advancing in rank at that point in my life, I said 'Call me Commander,' " Robinson said, good-naturedly, "and it stuck."

Reach Paula Rath at paularath@aol.com.