Some things should go without saying. But sometimes we need to say them anyway.

Here are two: You can’t stop exercising as you grow older. And if you’re 50 or so, and you’ve never adopted a fitness regimen, you’d better start.

Both ideas seem so blindingly obvious, so utterly axiomatic for the self-involved baby boom generation of which I am part, that I’m still not sure why anyone needs to be reminded. But the numbers tell a different story.

According to the National Institute on Aging, only 25 percent of people age 65 to 74 engage in any kind of regular physical activity. For people 85 and older, it’s just 11 percent.

Does it seem unreasonable to ask an 85-year-old to exercise regularly? It shouldn’t, because it isn’t.

“At age 85, you want to continue enjoying life and not be limited by your physical abilities because your muscles aren’t strong and you’re having balance problems,” says Chhanda Dutta, chief of the clinical gerontology branch of the National Institute on Aging. “There’s so much more to life than simply being able to dress yourself.”

About two weeks ago, the NIA launched a major campaign to help older Americans start, or continue, exercising despite the obstacles that aging inevitably throws at us. (And here I note that by “older” the agency means people over 50, which includes me. Not sure how I feel about that.) Whether you have a heart condition, you think you’re too busy, you’ve spent a lifetime on the couch eating curly fries, you find exercise to be drudgery, or you’re afraid you might hurt yourself working out, the Go4Life campaign is not taking no for an answer.

“I think that a lot of people may not know where to begin,” Dutta says. “And the other thing is we all lead busy lives, and what we are doing with this campaign is trying to show people that there are ways they can incorporate exercise and physical activity into their busy lives.”

The centerpiece of the campaign, the agency’s new Web site, is designed to rectify that. It contains more specific exercises, motivational tips, advice, health and nutrition information and success stories than you’ll ever need. It should. It is based on NIA research and the recommendations of a panel of experts; the program took two years and $3.1 million to develop. The NIA also is partnering with 29 public, private and nonprofit organizations — from the U.S. Chamber of Commerce to the American Medical Association to Sunrise Senior Living — to spread the word.

What it all boils down to is pushing past the perceived obstacles to fitness. The primary one, according to Tom Prohaska, a professor of public health and aging at the University of Illinois at Chicago, is that many older adults “don’t think they are capable of exercising or exercising safely” because of health conditions. Actually, he said, studies show that fully 95 percent of older adults, including those with arthritis, hypertension and heart disease, can safely work out when shown how.

Older people also are convinced that exercise won’t benefit them. “Some people don’t realize . . . that the things they attribute to normal aging are really because they aren’t physically fit,” says Prohaska, who helped develop the Go4Life program.

There are programs for just about everyone — for the homebound, for the chairbound, for people who need to get restarted after a health setback. Various groups are trying to solve one of the most difficult problems — providing lower-income elderly people ways to work out in unsafe neighborhoods. Another approach is to incorporate movement and physical activity into daily life, instead of making it a chore that must be done each day. Connecting with a workout buddy — for seniors this is often a walking partner — makes it all much easier.

For the record: You need to exercise for the rest of your life, not just to maintain cardiovascular fitness, but to keep up your strength, balance and flexibility. If you do, you’ll help prevent heart disease, high blood pressure and diabetes. You may maintain mental agility longer. You’ll have more energy. Your mood may brighten. You could meet other like-minded people.

Or, like most people over 65, you can ignore this advice. It’s up to you.