Jim Owen, a 78-year-old former Wall Street workaholic, was a couch potato eight years ago.

“At 70, I looked in the mirror and said, ‘I’m an old man,’” he remembers. He’d read a statistic that people who make it to age 70 could expect to live another 15 years. “I thought, ‘If I look like this now, it’s all downhill from here,’” he says.

Now, he tries not to let two days go by without some kind of movement. He bemoans the number of Americans who suffer from lifestyle-induced chronic illnesses and blames a fatalistic mindset that often comes with age. “If you want to change behavior, you have to start by changing perception,” he says. “The perception is when you’re older, you’re weak, your best days are over.”

Owen argues that he’s now in the best shape of his life. He couldn’t do one pushup when he started. Now he does three sets of 50 once a week.

He discusses his evolution—both physical and mental—in his book, Just Move: A New Approach to Fitness After 50, and at lectures around the country. He also has a website, justmoveforlife.com.

“The reason a lot of people don’t start this journey is there’s a lot of conflicting advice out there,” he says. “Should you do high-intensity or slow walk? The other problem is most of it is aimed at a younger demographic. There’s nothing wrong with that, but when you get to be 70, it’s not about the vanity stuff; it’s ‘How do I get rid of aches and pains, how do I build a life for myself?’”

The answer, he says, is “One step at a time.”

“Don’t worry about how far or how fast, just get off the couch and walk,” he says. “On Day 1, I could not walk for 20 minutes without huffing and puffing. So I’d go maybe five minutes. I did that for 30 days, just to make it into a habit. Now I don’t even think about it. Moving is a natural part of my lifestyle. Once you see some results it goes from ‘I can do this’ to ‘I will do this.’”

Owen, who is adopted and doesn’t know his birth family, doesn’t dwell on the consequences of genetics. Health with movement—up to and including recovery from unexpected health problems. “I don’t want to sit here and talk about living longer—I’m not sure you can do much about that,” he says. “But you can live a better quality of life if you get off the couch.”