An ageing former prime minister who predicts he might not live until 2020 was formally appointed head of the committee organising Tokyo's Olympic Games on Tuesday.

Yoshiro Mori, a 76-year-old rugby enthusiast, had already accepted an informal offer from Japan's education minister after initially rejecting overtures on the grounds of his age.

"I am going on 77 this year," he told a seminar hosted by Kyodo News. "I am destined to live five or six more years if I am lucky. This will be my one last service to the country." said Mori, who has been president of the Japan Rugby Football Union since 2005.

His age stands in sharp contrast with that of two-time Olympic 1,500-metres gold medallist Sebastian Coe, now 57, who led London's bid for the 2012 Summer Olympics and headed the event's organising committee.

Carlos Arthur Nuzman, 71, a Brazilian lawyer and a former volleyball player, is president of the organising committee for the 2016 Summer Games in Rio de Janeiro.

Mori, who served as prime minister from 2000-2001 with his tenure shortened by a series of gaffes, is still a member of the lower house of parliament.

He also led the Japan Sports Association for six years until 2011, helping Japan's successful bid to host the 2019 Rugby World Cup.

He has also been credited with using his contacts with foreign government leaders in mustering support for the Tokyo 2020 bid.

He told the seminar he would try to make the 2020 Tokyo Games "an Olympics for a new age".

The Tokyo metropolitan government and the Japanese Olympic Committee are due to launch the organising committee on January 24.

Tokyo, which hosted the Summer Olympics in 1964, has touted a "compact" Games, with 85 percent of the venues located within eight kilometres (five miles).

It beat other bidders Madrid and Istanbul -- despite the country's on-going struggle to recover from the 2011 earthquake and tsunami disaster and the ongoing crisis at the crippled Fukushima nuclear power plant.

The upper echelons of Japan's political and business life are largely populated by older men.

It is not unusual for large corporations to have men in their 70s at the helm and the same generation is well-represented in the houses of parliament.