"Harry: So if I go back in time and kill my grandfather, what happens?
Vadderung: He beats you senseless, I suspect."
― The Dresden Files
"Even his experience doesn't compare to mine."
― Chiyo (Naruto)
"Mightily Oats: You're really going to let a little old woman go out and fight monsters!?
Mob: Why should we care what happens to a bunch of monsters? "
― Terry Pratchett, Carpe Jugulum
"Dead almost 20 years, you're still taking me to school..."
― Tony Stark (Iron Man 2)
The ability to be in top condition while at an old age. Opposite to Child Prodigy.
The user has great status both mentally and physically despite their old age either from years of training or off the fly making their opponents often underestimate them as well and they make it appear as if time has had no effect on their physical condition making them a force to be reckoned with. Some users have great intellect and are capable of being master strategists as well.
Maz Koshia (The Legend of Zelda: Breath of the Wild)
Shun Di (Virtua Fighter)
Ana Amari (Overwatch)
Albus Dumbledore (Harry Potter)
Minerva McGonagall (Harry Potter)
Lord Voldemort (Harry Potter)
John Wakefield (Harper's Island)
Superman (DC Comics)
The Batman of Earth-31 (DC Comics)
Deathstroke/Slade Wilson (DC Comics). Despite being around 60 years old, he is considered the greatest mercenaries of all time due to a failed medical experiment he had volunteered for when he joined the military.
Judge Dredd (2000 AD)
Max Tennyson (Ben 10)
Hex (Ben 10), a master magician at age 62.
The Avatars (Avatar:The Last Airbender/Legend of Korra) of the past.
The White Lotus (Avatar:The Last Airbender)
Iroh (Avatar:The Last Airbender) the Dragon of the West.
Splinter (Teenage Mutant Ninja Turtles)
Master Yoda (Star Wars), considered to be one of the most skilled users of the Force in the universe.
Despite his advanced age, Genryūsai Shigekuni Yamamoto (Bleach) was considered to be the strongest Soul Reaper in existence for the last millennium.
Ichibē Hyōsube (Bleach) is one of the oldest Soul Reapers, possibly older than even Yamamoto, and is also one of the strongest beings in existence.
Yhwach (Bleach) is the first and most powerful Quincy to have ever existed.
Though not as powerful as he was in his prime, even in old age, King Piccolo (Dragon Ball) wields frightening power, easily outmatching Goku and beating him to the point where his heart temporarily stopped.
Despite his advanced age, Master Roshi (Dragon Ball) is a very skilled and experienced warrior, enought to earn the respect of the God of Destruction.
King Bradley/Wrath (Fullmetal Alchemist manga/Brotherhood) is a very strong swordsman despite his body often feels the effects of old age.
Walter C. Dornez (Hellsing)
Tsunade (Naruto) appears to be a young woman, but she is already in her 50s, using her superhuman strength and a transformation technique to mask her physical appearance.
Despite being 91-years-old, Kakuzu (Naruto Shippuden) is one of the most powerful and dangerous member of the Akatsuki.
At the age of 68, 'Big Mom' Charlotte Linlin (One Piece) is one of the four most powerful pirates in the world.
Brook (One Piece) is a veteran 90 years old pirate and a master swordsman.
Despite being a blind elderly man, Fujitora (One Piece) is a extremely powerful Marine Admiral.
Despite his age, Garp (One Piece) is still considered one of the strongest marines alive.
Kureha (One Piece) is a genius doctor who has lived up to the age of 141.
While over 70 years old, Silvers Rayleigh (One Piece) is still one of the strongest people in the world.
Despite being nearly 80 years old, Sengoku (One Piece) was a Fleet Admiral of the Marines and one of, if not the strongest amongst their ranks, able to even battle the feared Blackbeard Pirates by himself.
All Minks (One Piece) are natural born fighter who retain their physical prowess even in old age.
Though elderly, Nekomamushi and Inuarashi (One Piece) are the strongest of the Mink tribe.
Despite his age, Whitebeard (One Piece) was still considered one of the most powerful men in the world before his death.
Despite being elderly, Hayato Fūrinji (History's Strongest Disciple Kenichi) is a powerful martial artist in prime condition.
Cologne (Ranma ½) looks like a deformed she-gnome, measures her age in centuries rather then years, and can still beat down any two of the teenage martial artists at the same time.
Happosai (Ranma ½) one of the two by-far most skilled characters in the series, and likely easily the most powerful chi-user.
Though not as powerful as she was in her prime, Genkai (Yu Yu Hakusho) remains a formidable fighter.
Despite his old age, Bang (One-Punch Man) is ranked 3 among the strongest of the Hero Association and founder of his own brand of martial arts.