What's the key to a long life? UnitedHealthcare released its annual 100@100 survey of 100 people who reached the enviable age of 100 and found that attitude is a major factor.

One in four centenarians said that a positive outlook is the most essential element for living a long healthy life, and more than six in 10 said they were positive people.

Diet and exercise were also thought to be vital elements, with 21 percent identifying a good diet as the key element of healthy aging, and 10 percent saying that regular exercise was the main route to a long, happy life.

Centenarians walk and strength train weekly for exercise, while 46 percent saying they walk or hike, 34 percent report doing exercises to strengthen their muscles. And 29 percent say they meditate or participate in other activities to relieve stress.

Proving that age is just a number, 60 percent of centenarians said they didn't feel old, and those who admitted to feeling old said they started feeling old, on average, at the ripe old age of 87. Almost half — 47 percent — said it got easier to maintain a positive outlook as they aged.

How old do they feel? On average, a youthful 79. Not surprisingly, family was very important to them, with 97 percent calling family a top priority.