The lifespan for many sporting stars can be cruelly short - in few professional fields do people hitting 30 get described as "veteran".
But across the Olympics, there is proof that age need not be a barrier to competing at the highest level.
Anthony Ervin, 35, US, swimming
Sixteen years on from winning gold in the 50m freestyle at Sydney 2000, Anthony Ervin has reclaimed his title, becoming the Olympics' oldest swimming champion at 35.
His "swimmer's burnout" period in between saw him pursue a love of rock music, battle personal demons and even sell his first gold medal to charity.
But he started to train again in 2011, making the London Olympics in 2012, and already had a gold medal from the 4x100m freestyle event at Rio by the time he lined up on Friday night.
On his latest gold, he said: "I'm keeping it for now. Who knows what the future holds?''
Katherine Grainger, 40, GB, rowing
With a silver alongside partner Victoria Thornley, Grainger has become Team GB's most decorated female Olympian.
After finally winning gold at the London games, after three attempts, Grainger took two years off to study for a PhD.
She endured a difficult build-up to Rio, with reports she and Thornley had fallen out and suggestions it might be a games too far. All this is why she described the silver as her "greatest achievement".
There are no plans, though, for a shot at Tokyo 2020, with Grainger telling her parents, "I won't put you through it again."
Oksana Chusovitina, 41, Uzbekistan, gymnastics
Gymnastics is a sport that traditionally favours youth - Aly Raisman, captain of the all-conquering US team, has the nickname "Grandma" at the grand old age of 22.
But one woman bucking that trend is Oksana Chusovitina, who first competed in the 1992 Olympics in Barcelona, and has been at every Summer Games since.
She remains a top-level competitor too, making the vault finals in fifth place against rivals some of who weren't even born when she made her debut.
"When I was younger, I was quicker and I ran and never got tired," she told the BBC before the games.
"Today, of course, things are different. Now I train with my head."
Hoang Xuan Vinh, 41, Vietnam, shooting
While gymnasts tend to be young, shooting and equestrian have broader age ranges, with competitors having the highest median age of participants.
Proving this point, Vinh gained Vietnam's first-ever Olympic gold in the men's 10m air pistol event at the start of the games.
He also won silver in the men's 50m pistol event.
It delighted his home nation, with Vietnam's sports minister saying he had "gone down in history".
Kristin Armstrong, 43, US, cycling
At the time trial last Wednesday, Armstrong became the first cyclist to win three consecutive golds in the same event. Her experience proved crucial on a difficult course.
She was the oldest competitor in the event, and has been in the sport long enough to retire - twice. Her victory came a day before her 43rd birthday.
At home in Boise, Idaho, she works as a community health advocate, finding time to train alongside raising a family.
Asked why she still wants to compete, she said: "Because I can."
Lesley Thompson-Willie, 56, Canada, rowing
When Thompson-Willie took her seat as coxswain with Canada's women's eight rowing team, she tied the record for most appearances by a woman at a games, at eight.
The role involves tactics, motivation and navigation. Coxswains have to be strong enough to sit still in choppy waters and keep their weights to strict limits.
"I think it's redefining to our society that we can keep going, as long as we're active," she told the Globe and Mail.
"Hopefully it's a sign of the importance of being fit and being able to keep participating in things."
Julie Brougham, 62, New Zealand, equestrian
There are several equestrian competitors in their sixties at Rio, but the oldest, both in the sport and across the whole games, is Julie Brougham.
It is her first Olympics and she is only the third rider to represent New Zealand at that level.
She missed out on qualification in the dressage, finishing 44th.
But with Japanese equestrian Hiroshi Hoketsu competing at the London games aged 71, she could still have another shot at glory next time.