However, mystery surrounded his birthday. Estimates of his age ranged between 33 and 42. Yifter was coy on the issue, telling reporters: "I don't count the years. Men may steal my chickens. Men may steal my sheep. But no man can steal my age."
Willis' achievement at Rio completed New Zealand's best Games medal haul for 30-somethings.
Rowers Hamish Bond (30), Eric Murray (34) and Mahe Drysdale (37) won golds, and Rebecca Scown (33), Valerie Adams (31), Huriana Manuel (30) and Jo Aleh (30) took silver in their respective rowing, athletics, sevens and sailing disciplines.
Their success indicates the current system, through performance enhancement grants, offers athletes better financial support than the past and allows them to compete into their later years.
Athletes can delay settling into non-sporting jobs to support families or advance up employment ladders.
Few athletes are better positioned than Willis to run for their livelihood. He prefers to travel with his family and negotiates with his sponsors and agent to get apartment deals in lieu of staying in traditional athlete hotels.
Take the Monaco Diamond League event last year, when Willis bettered his New Zealand 1500m record for the fifth time in 10 years with a time of 3m 29.66s. He finished fifth and earned US$2500 ($3423).
Willis stayed less than a finishing straight sprint from Stade Louis II on the French side of the Monaco border. He warmed up on a jetty leading to a phalanx of multi-million-dollar launches, before strolling up the street into the stadium.
As he said: "The All Blacks wouldn't prepare in the same locker room as their opposition."
His record justified the method.
Willis has raced in Europe since 2001 but, as Rio showed, his body can still foot it with youth.
"I'm surprised to be feeling so energetic in my legs, which indicates I might be able to keep handling the rigours of training," he told the Herald on Sunday last year on the French Riviera. "I think the statistics around age are skewed by an amateur era when people did sport until it was time to get a real job. Professionalism means people can dedicate themselves longer."
Willis is proving his hypothesis true.
In fact, before the Rio 1500m denouement, he admitted to being affected more mentally than physically in a tweet.
"I had to fight doubts 20 mins before the final. Thinking of my son watching on tv brought me back to a thankful state of mind."
His achievement must rank among New Zealand's finest at the 31st Olympiad, regardless of medal colour.
Willis has subsequently called time on his 2016 season, one in which he triumphed in his craft but also continued a vocal crusade against drug cheats and articulated his catharsis at overcoming a porn addiction.
Willis, with his forthright views and willingness to engage directly with his fanbase via social media, remains one of the few New Zealand athletes capable of making a genuine difference to people's lives beyond generating the feel-good nationalism of sporting achievements.
Thankfully, fans look set to receive the benefits of his wisdom for at least four more years in the public eye.
Oldest Winners:
An Olympic gold medal (men): Oscar Swahn (Sweden), 1912 single shot running deer team* - 64 years, 8 months, 15 days
An Olympic gold medal (women): Eliza Pollock (USA), 1904 team archery - 63y, 10m, 29d
A Formula One grand prix: Luigi Fagioli (Italy), 1951 French GP - 53y, 22d
A golf major: Julius Boros (USA), 1968 PGA Championship - 48y, 4m, 18d
A heavyweight boxing championship: George Foreman (USA), 1994 WBA and IBF titles - 45y, 9m, 26d
A cycling grand tour: Chris Horner (USA), 2013 Vuelta a Espana - 41y, 10m, 23d
A New Zealand Olympic gold medal (men): Mahe Drysdale, 2016 Rio single sculls - 37y, 8m, 25d
An open era tennis major (men): Ken Rosewall (Australia), 1972 Australian Open - 37y, 2m, 1d
An Olympic 5000m title: Miruts Yifter (Ethiopia), 1980 Moscow - 36y, 2m, 17d**
An open era tennis major (women): Serena Williams (USA), 2016 Wimbledon - 34y, 9m, 13d
An Olympic 1500m title: Albert Hill (Great Britain), 1920 Antwerp - 31y, 4m, 26d
A New Zealand Olympic gold medal: Georgine and Caroline Evers-Swindell, 2008 Beijing double sculls - 29y, 10m, 6d***
* - No animals were harmed in the making of this medal. A deer-shaped target made 10 runs of 75 feet, with the gunman firing one shot during each run.
** - Mystery surrounds Yifter's age, with wild estimates varying from 33 and 42. He refused to give a definitive answer, telling reporters: "Men may steal my chickens; men may steal my sheep. But no man can steal my age."
*** - Technically, Georgina was older by four minutes