Cracknell will occupy the number two seat and only a few weeks shy of his 47th birthday, will become the oldest man to take part in an event which dates back to 1829. 

"If I can make it to the starting line, it will be the proudest thing I have done in rowing," he said. 

Perhaps not surprisingly, he has jokingly been dubbed "Old Man River".

It will be 19 years since he first won Olympic gold. 

Some of his crew-mates in a fortnight’s time were scarcely out of the cradle when he rowed to glory alongside Sir Steve Redgrave in Sydney.

Cracknell cheerfully admits "I am older than some of the guys’ dads".

It is the latest challenge for Cracknell, who once rowed across the Atlantic with adventurer Ben Fogle.

His career has echoes of another university oarsman Lord Desborough, who rowed in the fabled dead heat race of 1877, later climbed the Matterhorn by three different routes and twice swam across the base of Niagara Falls. 

Desborough, the leader of the 1908 Olympic Organising Committee, was an international fencer into his 50s.

It takes a special kind of competitor to excel at elite sport after the age of 40, but the roll of honour is a long one.

Those who do so in an endurance sport are particularly notable.

American Kristin Armstrong retired after winning time trial Olympic gold in both Beijing and London. 

But the lure of competition proved too strong and she pulled on the Lycra for one last tilt at glory in 2016.

"I left the sport on top twice now – something keeps driving me back," she said.

The pressure was on when she set out with her closest rivals already on the course on a wet and windy day in Rio.

"I kind of tricked my mind to give myself confidence" she admitted afterwards. 

She chased down the time set by Russian Olga Zabelinskaya to achieve her dream of a third Olympic gold.

Rio did not quite have the same fairytale end for 42-year-old Hungarian fencer Geza Imre, who came within a touch of winning Olympic epee gold. 

In the end, he lost to Park Sang-young of South Korea, a man half his age.

Even so, Imre’s achievements over the previous year had already struck a number of blows for the over-40s.

His first world title had come in Moscow at the tender age of 41 and there is certainly something about Hungarian fencers maturing with age.

The legendary Aladar Gerevich, a recipient of gold for the first time in 1932, won his last as part of the team at Rome 1960, aged 50.

In 1968, George Foreman won gold in the Olympic boxing ring and later beat Joe Frazier to become world heavyweight champion before losing to Ali in the ‘’Rumble in the Jungle.’’ 

Foreman returned the ring in his late 30s, challenged the younger Evander Holyfield at 42 and beat Michael Moorer to win the International Boxing Federation and World Boxing Association (WBA) titles aged 45.

He retired aged 48.

Only Bernard Hopkins was older when he defeated Beibut Shumenov to win the WBA light heavyweight title aged 49 in 2014. 

Hopkins lost his final pro bout less than a month before his 52nd birthday.

Many will hope that boxing reverts to a younger fighter’s game in the future.

In the 1970s and 80s, the top-level career of a swimmer was notoriously short but American Darra Torres bucked the trend. 

She had won the first of four relay golds in 1984 and in 2008, she was still there and competing in her fifth Olympics at 41. 

It was an extraordinary achievement in a sport where many of the competitors were half her age. 

She won three silvers at the Water Cube in Berlin to set the seal on her career.

As a rule, gymnastics has an even lower retirement threshold than swimming but Oksana Chusovitina competed in the 2016 Games at the age of 41.

She had begun as a teenager before the break-up of the Soviet Union, won gold as part of the Unified team in 1992 and went on to represent Germany and then Uzbekistan in a remarkable career at elite level.

Chusovitina has still not given up on an appearance in Tokyo aged 45.

In football, Sir Stanley Matthews won his 54th and final England cap in their World Cup qualifier against Denmark in 1957, aged 42. 

He was renowned for his remarkable fitness and continued playing club football at the top level with Stoke City beyond his 50th birthday.

It was a measure of his calibre that legendary Russian goalkeeper Lev Yashin and Real Madrid superstars Raymond Kopa, Alfredo Di Stefano and Ferenc Puskas lined up in Stoke for a testimonial match in April 1965. 

At the end, Matthews was chaired off as the crowd sang ‘’For He’s a Jolly Good Fellow.’’

A man of similar age made a remarkable international football comeback in September. 

Former FIFA world player of the year George Weah had been sworn in as Liberia’s head of state a few months before.

The crowd were astonished to see him leading out the national team against Nigeria a few days short of his 52nd birthday. 

He lasted 79 minutes but could do nothing about the result – Liberia lost.

Roger Milla had been an ‘’Indomitable Lion’’ for Cameroon in the 80s and 90s but at 42 he was still part of the side at the 1994 World Cup in United States. 

Although he scored within a minute of his final appearance, he was unable to prevent a 6-1 defeat against Russia .

Playing outfield beyond 40 is very demanding but the 40 club of goalkeepers includes Northern Ireland’s Pat Jennings, England’s Peter Shilton and Liverpool’s Zimbabwean Bruce Grobbelaar.

Gianluigi Buffon is still going strong with Paris Saint-Germain at 41 and yet no one has quite matched the achievement of Buffon’s Italian compatriot Dino Zoff.

He was 40 when he captained his country to victory in the 1982 FIFA World Cup, the high point of an outstanding career which lasted another year.

The physical demands of rugby union have made longevity less of a phenomenon.

Even so, Uruguayan number eight Diego Ormaechea pulled on the powder blue shirt during the 1999 Rugby World Cup aged 40 years and 26 days.

He even scored a try against Spain and also turned out against South Africa.

The great Australian cricketer Don Bradman was in his 40th year when he captained his country on their unbeaten tour of England in 1948. 

By Australian standards, he was a veteran but the dominant 19th-century cricketer Dr William Gilbert Grace played his last Test Match for England in 1899 aged 50 and Wilfred Rhodes, of a slightly later vintage, was still playing Test cricket aged 52.

In the 70s, age was sometimes favoured over youth. 

Brian Close, then 45 years old, was recalled by England for a particularly grueling Test series against West Indies. 

The most stark episode came in Manchester. 

Close and John Edrich, combined age 84, opened England’s batting and were confronted by a fierce barrage of short-pitched bowling by the Windies' fearsome fast bowlers. 

"Cricket came close to a blood sport," said The Cricketer magazine.

Equestrianism routinely provides some of the oldest competitors at the Olympic Games. 

British dressage rider Lorna Johnstone celebrated her 70th birthday during the 1972 Munich Olympic Games.

The official report notes she "performed exceptionally to join the final 12".

She remains the oldest female Olympian.

In Rio, Sir Mark Todd of New Zealand just missed out on a team medal in the three-day event, competing in his seventh Olympics at the age of 60. 

Nick Skelton of Great Britain astounded the world of show jumping with his magnificent clear rounds to gold in Rio aged 58.

And he was not even the oldest in the field – team-mate John Whitaker was 60 and another half a dozen riders were also over 50.

Earlier, Ian Millar of Canada had competed in the jumping at London 2012, his 10th Games, aged 65.

In 1908, the British archer Sybil Newall, known as ‘’Queenie’’, secured Olympic gold at the age of 53. 

To this day, she remains the oldest woman to win gold and did so while wearing an ankle-length dress.

But the grandfather of them all was Oscar Swahn of Sweden. 

Born in 1847, he was 64 years old when he won gold in the team event for running target at the 1912 Olympics in Stockholm.

He was also part of the Organising Committee for the Games.

Swahn was still competitive eight years later and won silver for Sweden in the men’s running target double shot aged 72 years and 279 days..

By this reckoning, Cracknell will probably still need to be in contention around the year 2045.