PANAMA CITY – Striding around Panama City on tree-trunk legs that have carried him through 66 countries, 80-year-old US citizen Harry Lee McGinnis reckons he knows the secret of staying healthy into old age.

"Movement," he explains, as he readies for the final stage of an 80,000-mile around-the-world walk that has taken him 18 years so far, inspired by glossy photos of foreign lands he pored over as a child.

A towering figure with a muscular build and the rugged looks of actor Roger Moore, McGinnis is not your average old-age pensioner.

"Moore and I are the same age, but I think he looks older," he jokes.

Strolling up Panama City’s skyscraper-lined Avenue Balboa, McGinnis puts his nomadic retirement down to a deep curiosity about the world, which comes through as he chats about everything from the Chinese economy to nanotechnology.

"I grew up in a time of adventure, with films like Marco Polo and stars like Errol Flynn," he said.

Born in rural Indiana in 1927, shortly before the great depression, McGinnis’s grandparents taught him to read before he started school by studying National Geographic magazine.

They sparked a stubborn wanderlust that has seen McGinnis spend the last two decades on his feet, accompanied by a huge steel-tipped wooden staff and a 100 lb (45 kg) backpack.

Nicknamed "Hawk" during his time as a World War Two army sniper in east Asia, McGinnis never settled into the domestics of everyday life. He married and divorced five times.

After spells as a bandleader, a country club manager and a Methodist minister, he embarked on his first expedition in August 1983, aged 55, setting off on a four-year walk across the 50 states of the continental United States.

After a five-year lull, during which he gave marriage one last shot, he decided to get back on the road, funded by his army pension and sponsors who donated some equipment.

This time McGinnis began a worldwide trek, choosing Dublin’s St. Patrick’s Day parade of 1992 as the starting point. Continental Europe, Africa, Asia and South America followed. "I have only flown seven or eight times when it was necessary," he said.

Fans chart his progress on his Web site, www.hawkwalk.com, which describes how he sets up his tent and camping stove by roadsides or in church foyers and mentions his brushes with knife-wielding assailants in north Africa.

"Hawk is simply the most interesting person I have ever met," said Bob Ehrenheim, who was teaching English in Ethiopia in 1996 when McGinnis appeared and asked to use the school’s gym and tennis courts. They are still in touch.

"He is very, very intelligent, and, well, he has to be a little bit crazy," Ehrenheim, who now lives in the United States, said by telephone while vacationing in Mexico. Now McGinnis plans to walk through Central America and Mexico before finishing up the walk in the United States, estimating he will reach Texas in around 2010 or 2012.