LYON, France (Reuters) - A French centenarian became the fastest cyclist of his age on Friday when he covered 100 km (62 miles) at an average speed of just over 23 km/h.

Robert Marchand, a former fireman and boxing enthusiast from Paris, who will celebrate his 101st birthday in November, had been training every day for months to cross the finish line in under five hours.

"I did better than expected," he told reporters at the velodrome in Lyon, southeast France, where he completed the 300 laps in 4 hours, 17 minutes, 27 seconds, averaging 23.305 km/h.

Marchand's uncommon vitality has piqued the interest of scientists at the Inserm public research institute who have examined him every three months to try to understand the secret to his longevity.

The wiry centenarian, who weighs in at just 51 kg (112 lbs), says he never smoked, but otherwise indulged a healthy appetite for wine and women throughout his life.

(Reporting By Catherine Lagrange; Writing by Nicholas Vinocur)