Tsunade herself would count, were it not for the transformation technique that keeps her looking like she's in her late twenties/early thirties at all times. Without it, she apparently looks even older than she really is (we only ever see a badly wrinkled arm) thanks to her Creation Rebirth technique.
For the record, her actual age is early-mid 50s.
Orichimaru also counts as he was quite the bishonen when he was younger.
Genkai from YuYu Hakusho. Conclusively proven due to her ultimate technique having the side effect of temporarily shifting her back to her younger state.
Miss Maria Graceburt from Mai-Otome. And she reverts to that youthful look of hers whenever she activates her Otome powers, much to everyone's shock.
In Fushigi Yuugi, Tokaki and Subaru are an elderly couple that the heroes meet late in the story. They're actually two warriors of Byakko who fought several decades before; when Subaru uses her power to manipulate time, they can revert to their younger forms.
Hellsing: Walter C Dornez, Sir Integra Hellsing's butler, as revealed in The Dawn, was quite the bishiebadboy back during the Second World War. He gets his looks and youth back after he joins Millennium and becomes a vampire.
Though, this example, in-universe at least, could be considered an inversion because the only person who ever comments on his looks is Alucard, who claims that he was much more beautiful as an aged man.
To Love-Ru has Honegawa-sensei getting hit with de-aging alien skunk spray.. This happens.
Otose, the landlady from Gintama, is a perfect example.
So is Michiko Menezes from Michiko to Hatchin. Unfortunately not only her looks changed for the worse.
Tenchi's father Noboyuki in Tenchi Universe is shown to be so attractive in his youth that Ryoko is even smitten with him when the cast goes back in time for the movie Tenchi In Love.
Katsuhito, Tenchi's grandfather in several incarnations of the meta-series was handsome when young. In Universe and the original OVA series, he is actually Ayeka's brother Yosho, a handsome Jurai nobleman who got stranded on Earth. He's been on earth long enough to age rather dramatically. Though this is a ruse in the OVA series and he is actually still just as youthful as ever.
Flit Asuno from Mobile Suit Gundam AGE is a very unique variant, in that we're introduced to him when he's still a young boy,◊ and he spends over a dozen episodes like this. However, this Gundam series' shtick is that the war they're fighting is one that takes nearly a century to resolve. So by the time Flit's son takes over, he looks like this.◊ And when his grandson becomes the protagonist, he looks like this.◊ Badass Grandpa indeed....
Emperor Charles di Britannia from Code Geass isn't exactly super ugly at age 62, but he certainly cut an impressive figure◊ when he was younger.
The third manga special in Karin shows the titular vampire's parents when they first met. Carrera was damn cute, and Henry was much better-looking, also—but perhaps even more so than Henry was his father, James, who was very handsome. (Although as of that point, James's only appearance had him dried up and dead, so anything would've been better than that.)
Near the end of the GS arc of Pokémon Special shows us a younger Professor Oak. He was really buff!
Yellow's uncle's brain breaks when he sees how attractive the old Day Care Lady used to be.
The epilogue of the manga version of Chrono Crusade shows us Azmaria Hendrich as a 90-year-old woman. She doesn't exactly look bad, but the mangaka opted to draw her rather realistically, making the contrast rather...striking.
The same omake also reveals that Balalaika was an adorable (and very shy) nine-year-old, and Boris was a Bishōnen before he joined the military. Dutch, meanwhile, takes off running before the omake even starts.
In Panty & Stocking with Garterbelt, the old woman who Panty Anarchy stays with during her time as a mortal shows a picture of herself as a young woman, and she looks rather similar to Panty. Given that she turns out to be an actor hired by Garterbelt, the picture may be fake.
As revealed in the flashback sequences, Gran'ma Ben of Bone was definitely quite the looker. Also a gender flipped version if you compare Lucius Down's one appearance in the flashbacks to his present appearance. Briar, Gran'ma Ben's undead sister, is a particularly extreme example.
After three volumes, readers of Courtney Crumrin and the Night Things were well used to Great-Uncle Aloysius looking like this◊. Then came the short story "Portrait of the Warlock as A Young Man", from Aloysius' days during either the twenties or the forties. Hot damn.◊
Frau Totenkinder◊ from Fables used to look like this. She is also one of the few people who willingly gave up being quite the looker because she eventually got fed up with the physical urges that came with being young.
H'el from H'el on Earth wasn't always a scarred, grey-skinned, black-eyed man. Flashbacks and a hologram show how he used to look like back on Krypton, when he was quite handsome.
In Somewhere In Time the protagonist meets a very old woman who begs him "Come back to me." She gives him a lovely watch, but dies that night. Later, when he sees a picture of a stunning young woman, he finds it is the old woman. So he decides to try to go back in time to meet her.
In Annie Hall, Alvy Singer's old aunt is noted to have been quite a looker once.
In Hannah And Her Sisters Hannah's mother Norma was very beautiful as a young actress. Since Norma is played by Maureen O'Sullivan, it is pretty well justified.
The protagonist's reaction in The World's End upon seeing his younger self: "Oh my God! I'm so cute!"
The witches in Stardust — when one of them uses the power of a star to regain her youth, she becomes much more attractive.
Lorraine in Back to the Future, as Marty discovers when he goes back in time.note Once the movie is over, her aging is softened by the effects of Marty's time-machinations.
Jennifer in Back To The Future Part II, as Jennifer and her older self run into each other in 2015.
Depending on how you see it, Biff was also quite the Mr. Fanservice in his youth.
Edna Turnblad, in the 2007 film version of Hairspray. On the Making of DVD extra, the wardrobe designer says that John Travolta wanted to play Edna as someone who was a real "buxom babe" in her day (hence the cinched waists, pencil skirts, and other outfits reminiscent of Sophia Loren and other voluptuous actresses of the period). After she kicks Wilbur out, Edna cries over her wedding picture, which depicts a much younger, thinner Edna.
In the fantasy movie Willow, the sorceress Fin Raziel claimed that she was a young and attractive woman before she was turned into a a ferret by the Witch Bavmorda. The roguish hero Madmartigan therefore really wants to see her true form. Sadly, she had spent a long, long time in animal form, and when changed back to human, she found herself to now be a hag.
In Beerfest, we discover that Grandma was actually quite attractive when she came over from Germany. A very attractive whore. Erk.
In the film adaptation of Ray Bradbury's Something Wicked This Way Comes, we see the character of Miss Foley: an elderly spinster schoolmarm who longs to be her young, beautiful self again. Thanks to Mr. Dark, she gets her wish and turns into the beautiful blonde that she used to be ...with the added side-effect of blindness so that she can never appreciate her own beauty. Ahhhh, damn it all!
Darth Vader (as Anakin Skywalker), Obi-Wan Kenobi, Uncle Owen, and Aunt Beru are all shown to be this in the Star Wars prequels.
In Coraline, Ms Spink and Ms Forcible were quite pretty back in the day, as Coraline saw in the Other World.
In the film version of Bram Stoker's Dracula, the titular villain is meant to be portrayed as such, albeit with a twist since we first see him as elderly and he becomes younger as the story progresses.
Jane Hudson from What Ever Happened to Baby Jane? whose angelic good looks were whittled away over the years by a combination of alcohol and depression. Her sister Blanche has also aged but looks relatively healthy.
Mater from Cars appears to be a rusty, beaten-up tow truck, but whenever we see him in a flashback, he's always a shiny blue colour!
In Kontroll, Bela (a fat greying train driver) and Szofi are father and daughter. They have a scene together in which she tells him "You remind me of an angel," and he replies "You should have seen me in my prime!" They laugh.
Anyone who's been to Azkaban, like Sirius Black or Bellatrix Lestrange, will presumably suffer from this as their health and appearance deteriorate. In the movies, though, these characters suffer from Adaptational Attractiveness even after their stints in Azkaban.
Granny Weatherwax also, although she was "handsome" or "striking" rather than "beautiful". Even in the current stories' time she's not the stereotypical ugly old witch, having good teeth, good posture and an average-size nose (much to her annoyment).
As stated above, Miss Spink and Miss Forcible, in Neil Gaiman's book Coraline, former music-hall artistes, now elderly and swathed in cardigans.
One chapter of Ray Bradbury's Dandelion Wine had a man fall in love with a beautiful girl by her photo alone, only to find out that the photo was taken a long time ago and that the girl is now an old woman. When the old woman learns of this after the two of them strike up quite a rapport, she tells him that they could probably have started a romantic relationship if not for their vastly disparate ages.
In Angela Carter's Wise Children, the protagonist and her sister are former dancers who used to have a lot of lovers, now aged; they're determined to defy this trope. When invited to a family reunion, they're nervous about going, fearing that people will pity the decay of their looks; but they dress up showily in a manner that emphasizes their best points (legs last well) and walk in boldly, not sure if the effect is ridiculous or fabulous; some reactions, at least, prove that the latter is the case.
Tolkien's "Silmarillion": In the Song of the Ainur, Melkor and Sauron were both spirits of "might and beauty". BEFORE they became ugly, all-powerful Physical Gods of Evil.
In Lois Lowry's Anastasia Krupnik books, the young-teenage heroine swoons over Gregory Peck, only to discover that the movies she's been watching are decades old.
Sophie in Howl's Moving Castle suddenly experiences the transition from beautiful youth to leathery age when she is put under a spell.note Not being aware of her own beauty in the first place reduces the sting. Other characters thought she was Beautiful All Along.
In one of the Sammy Keyes books, Sammy finds an old picture of her cranky neighbor Mrs. Graybill, who was apparently quite pretty fifty years ago.
In John Dickson Carr's mystery The Demoniacs, the hero's girlfriend discovers that a certain very decrepit old-looking woman is younger than she looks — and might be her long-lost mother. The girl is quite upset by the possibility that she might come to resemble this hag.
In Agatha Christie's novel, The ABC Murders, when Poirot and Hastings see the dead body of the first victim, Alice Ascher an elderly storekeeper, Poirot notes that she must have been beautiful when she was young. Hastings doubts it, but later, when they find her wedding photo, he sees that Poirot was right.
In Stephen King's Misery, Paul is looking through Annie's scrapbook and comes across a picture of her when she was young, and notes that she was startlingly pretty.
In Bram Stoker's Dracula, the count invokes this trope to an extent. He at first appears decrepit and elderly, but he soon gorges himself on blood and appears youthful and perhaps even handsome, though since most of the novel is written from the protagonists perspective, he is described with less loving terms at times.
In Murder At Drumshee we hear about Gabor's previous marriage to Eithne and Mahon is shocked when he finally meets her. She is described as squat, sharp-featured and slightly overweight with dull mousy hair - he wonders how any man could have been attracted to her. Then at one point during the trial, her expression changes and the narration says "and he could suddenly see remnants of beauty in this drab, middle-aged woman".
In A Song of Ice and Fire, the morbidly obese merchant prince Illyrio Mopatis reveals that the sculpture of the beautiful young bravo in his courtyard was him at the age of 16.
For that matter, Robert Baratheon was apparently a muscular, broad shouldered, clean-shaven, long haired, handsome heroic figure who captured the hearts of many young women. However by the time we meet him in the present he has none of these traits left. His bastard son Gendry resembles Robert as a youth, which causes many of Robert's old acquaintances to double-take when they meet him.
Seeing as the Great Houses of Westeros all seem to have really good genes, several nobles that aren't described as attractive are this. Catelyn remembers her sister Lysa as a pretty girl before she let herself go.
In the Incarnations of Immortality series, Niobe Kaftan was considered the most beautiful woman of her generation. In her middle age, she let herself go because she lost her second husband and no longer cared about her looks. When she becomes an Incarnation of Fate, she chooses not to regain her old looks even though she can at any time. One of the only times she regains her old looks is when she gets seduced by Nicolai. The elderly Nicolai says that when he was young, he could very easily imitate a woman and seduce all the men around him.
Live Action TV
Howard's mother, Mrs. Wolowitz from The Big Bang Theory had never appears on screen, but she's described as an overweight women with facial hair. She told Sheldon tearfully that she was quite a looker when she was young as men would wait in line showering her with gifts of candies (which she ate them all).
In an episode of Family Matters, Eddie's grandmother Estelle does a photo show-and-tell for his class, revealing that Grandfather's plane back in WWII was called the "Brown Bombshell." Which may have been named after her, as the next picture she shows is of herself as she was back in those days - her knock-out looks are enough to get a reaction from the rest of the boys in the class. Eddie is mortified, but Estelle waves it off ("Ah, let the boys express themselves.").
Annette O'Toole's role in Smallville as Martha Kent reminded more comic readers (and artists) that she wasn't always a grey-haired middle-aged woman, which was subsequently used in a Superman reboot when she was portrayed as a rather attractive woman in Clark's younger days. Oddly enough, take a look at Annette O'Toole in 1983's Superman III where she plays Lana Lang. Cuter than Margot Kidder's Lois Lane by a Smallville country mile.
I.Q. From The Bugaloos was very handsome and to this day he is still good looking
Not that 30 Rock's Jack Donaghy is all that old or unattractive, but when he shows Liz Lemon a picture of himself at age 25, she tells him he used to have a chest like Superman and asks to keep the picture.
Not surprising considering we're talking about Alec Baldwin◊ here.
A Touch of Frost. Inspector Frost is going through a box of personal items stolen from an old lady, and finds some B&W photos of a voluptous young woman posing naked in the woods. The old lady just says "Oh, I was very naughty, wasn't I?" Frost just winks and says she'd better take this particular evidence home with her. "Else we might get too excited."
A poignant bit in Barney Miller when an older woman insisted that a local art gallery had "smut in the window". The smut in question turned out to be a tasteful nude portrait of herself in younger days. She'd been lovers with the now-dead artist, and the picture was a private endearment, never meant for exhibition.
The duchess from the It Takes a Thief (1968) episode "Lay of the Land", who was apparently the toast of Europe in her younger days. Noah mentions that she was "one of the most sought-after women of her day... sought after, and frequently caught." The episode's plot revolves around her Compromising Memoirs.
On 227 Pearl is the old lady who always sits at her window talking to her neighbors sitting on the stoop. One episode flashes back to the forties when she was young and hot.
In the BBC series I, Claudius, we see Augustus's wife Livia as a middle-aged woman, then an elderly widow, then an unbelievably old crone. But as she comments to Claudius late in life, she was quite the looker in her youth:
Claudius: The most beautiful in the world, they say. Livia: There was one other. But she was in Egypt. And besides, she didn't last as long as I have.
Charmed - The Charmed Ones had an enemy of the week who was an evil wizard. He modeled his handsome golem after himself as a young man.
Also in another episode their elderly aunt tried to get a demon to restore her youth and that of a few others. The various old people who are transformed become quite attractive 20-somethings.
Roger Sterling's tape-recorded notes for his memoirs in Mad Men provide a pretty darned funny pair of these. Apparently, back in the late '40s, Miss Blankenship—now a standoffish and somewhat prudish old spinster—was Bert Cooper's secretary, known to all in the office as the "Queen of Perversions." And Cooper himself? In his "sexual prime," apparently making quite a few conquests, before being, um, cut short by an unnecessary operation at the hands of a certain Dr. Lyle Evans (whom Roger believes Cooper may have had killed).
In The Thorn Birds elderly Mary Carson, in love with young priest, Ralph de Bricassart who rejects her. She bemoans that inside her old body she's still young. Mary is played by Barbara Stanwyck. If Ralph knew what she used to look like◊ he'd pray to God that the outside matched the in!
In a guest appearance on Law & Order: SVU, Carol Burnett played an aged actress and dancer. When Benson arrives at her home on the night she murders her husband, she is nostalgically watching her old films.
Burnett: See her detective? That's the girl I used to be.
In Community episode Basic Genealogy Britta unsuccessfully attempts to invoke this to get on Troy's Grandmother good side.
In an episode of That's So Raven, Eddie mocks a Star Trek-esque show, but goes to a convention in hopes of meeting the actress who played the attractive character "Curvatia". Unfortunately, since the show was quite old, the actress is now old and fat. Eddie shrugs this off and asks for her autograph anyway.
Susan and her mother Grace in My Family appear to consider themselves this, but both still get plenty of male attention despite being in their 50s and 70s respectively.
The Lady Cassandra and the Face of Boe from Doctor Who.
A Mash episode has Col. Blake put on trial after Majors Burns and Houlihan report him for "giving aid and comfort to the enemy". When Hawkeye and Trapper catch wind of this they crash the trial with Meg Cratty, an elderly American nurse who treats children from North and South Korea alike (and to whom Blake had donated spare medical supplies). After she testifies on Blake's behalf, an admiring Hawkeye leans over to her:
Hawkeye: You're beautiful.
Nurse Cratty: I used to be, sonny.
In Xena: Warrior Princess, Xena and Gabrielle find themselves 25 years in the future. The Xena lookalike Meg has let herself go. Gabrielle jokes that Xena should cut down on her food intake to prevent herself from going the same way.
In Coronation Street when Fred (who is in his seventies, bald and extremely overweight) was putting his picture up online, his friend asked who the man in the black and white photo was. It turns out it was a picture of Fred from his youth and he was quite the Pretty Boy.
Sid has claimed to have been in the 2003 Only Fools And Horses Christmas special "Sleepless in Peckham" when looking at himself in the photograph of the 1960 Jolly Boys' Outing.
"Dreams of the Everyday Housewife" by Glen Campbell.
Calvin's mom from Calvin and Hobbes. In this strip, Calvin finds an old prom picture, and asks his dad that who's that "bimbo" next to him. She turns out to be his mother.
9 Chickweed Lane - Edna O'Malley◊, now usually known as "Gran," relays to Juliette the story of how she and Juliette's father met during World War II. A young Edie Ernst was a USO performer, later OSS agent, and genuine bundle of hotness. She once reminisced about "that thing I had going with General Patton," causing her daughter to comment, "There's so much about the North Africa campaign I just don't want to know."
True of a lot of wrestlers. Many of them were quite attractive before getting into the business. Then the years of getting thrown around, endless travel and drug consumption (both medical and recreational) start taking their toll...
The phrase "The road has owned him/her" is often said.
Manager Paul Bearer, in the middle of a plot dump explaining he was carrying on with Kane and The Undertaker's mother, paused and explained to a totally-unbelieving interviewer that "I didn't look like this, then — in fact I was actually pretty studly!". Most viewers considered this unlikely. But pictures of Bill Moody as a young man show it to be true.
Mae Young, who most wrestling fans know as that revolting horny grandma, was quite the looker when she was young back in the 1950s. She actually modeled her look on the starlets of the time. Observe. WWE never used or even mentioned this, despite the fact that it could conceivably have made her older self funny (the idea being that she still acted like her younger sex kitten self, despite being in her eighties).
Mick Foley, believe it or not. Despite now looking like a scruffy teddy bear who's missing several teeth and one ear, anyone who's seen photos of him in his youth (generally from reading his autobiography) will see that he was a pretty good-looking guy before he started taking chair shots.
Ric Flair. Looks like a caffeine-crazed grandpa these days but he was a real looker in his youth.
Raven: Was known as a pretty boy early in his career, working under the name "Scotty The Body". Then the years of hardcore matches and legendary drug consumption started to become noticeable.
Tammy Sytch is a weird example. When she first showed up in the WWF, her looks were dazzling. Then her drug consumption (along with her partner Chris Candido's) spiraled out of control and she started looking very rough. Sometime around 2004, both Candido and Sytch kicked the drugs and she started looking pretty good again. Then Candido died in a fluke surgical mishap and Tammy went to pieces (understandably) and piled on the pounds. Now, having gotten her life straightened out again, she looks good.
As of her recent arrests, she seems to be playing the trope straight again.
One thing that made it really bad was the act of blading, taking a small piece of sharp metal and making a small cut in the forehead to help sell a match. Eventually, all those little cuts add up and leave a wrestler's forehead looking really rough. Ric Flair and Jerry "The King" Lawler are great examples (thankfully it's falling out of favor in recent years).
Inverted with Bull Nakano. In wrestling, she had a fat-but-tough build and wore punk rock looking clothes, bizarre makeup and more bizarre hair (Bobby Heenan infamously compared it to a porcupine). When she quit wrestling for golf, she dropped the weird outfits and hairstyles, lost a lot of weight, and is quite attractive.
Razor Ramon (Scott Hall) was once a pretty sexy dude◊, however time, the wear and tear of wrestling and rampant alcohol abuse has taken its toll◊ on him.
Played for drama with Ma-Ha-Suchi in Exalted. In the First Age, he was known as the "Wolf with the Red Roses", was ridiculouslyBishōnen, and had a Motivation of "Bed every Celestial Exalt." And he almost pulled it off. Then came the Usurpation, and he was forced to flee into the Wyld... where he ended up stuck in the form of a hideous goat-wolf-satyr... thing. No wonder he wants to destroy civilization.
Inverted in Into the Woods: the Witch, cursed by her mother, is prematurely old and shriveled when the play begins, and has been for some time. Her youthful, beautiful appearance, which is revealed at the end of Act One and continues for the rest of the show, is in fact her genuine current self.
Dr. Daly, the aging vicar in Gilbert and Sullivan's The Sorcerer. In fact, not only does he sing a melancholy song about how stunningly attractive he was as a young curate, he still makes one young female character go weak at the knees.
In On the Town, Madame Dilly cautions Ivy: "Sex and art don't mix. If they did, I'd have gone right to the top."
Juno's song "I Sleep Easier Now" in the Cole Porter musical Out of This World.
In Noël Coward's Bitter Sweet, we first meet the elderly Marchioness of Shayne in 1929, then flash back to 1875 when she, as Sarah Millick, eloped to Vienna with her singing teacher, Carl Linden. After an officer who was hitting on her killed Carl in 1880, Sari Linden became world-famous performing the songs he wrote. At last returning to England in 1895, she agreed to marry a Marquess who had been fondly pursuing her across Europe.
"My name is Jerbraz, once one of the most handsome and dashing members of my little circle of friends ... that is, back when I could be seen. Now I have to rely on my charm alone to make an impression ... that and this nasty sword that conveniently turned invisible with me. If you see someone's head just suddenly go flying off for no reason, it's not your imagination."
Although he never says as much, in Rogue Galaxy we actually see a younger Dorgongoa, who looks a bit like a younger, handsomer Conan the Barbarian. Consider his "present" form is a morbidly obese cartoonish pirate.
Kliff Undersn from Guilty Gear X can revert to his young form during a fight.
Revolver Ocelot: behold the earth-shattering sound of the fangirl's jaws dropping onto the floor when the young◊ Major Ocelot strolled onto the scene in the third game.
Roy Campbell. He looks like a fairly amiable old man in Solid Snake's timeline — but in Naked Snake's timeline he's a ruggedly-gorgeous young man◊ who isn't at all ashamed to use his sexuality to get what he wants.
Not to mention Solid Snake himself by the time the fourth game rolls around.
Don't forget either EVA/Big Mama in Metal Gear Solid 4.
Gary Golden and Imalia of Vampire: The Masquerade – Bloodlines. To the point that they're willing to pay generously for any footage of themselves from before their Embrace by the Nosferatu. Also, any other Nosferatu that fall under the heading of "Cleopatras."
Can't forget Kreia from the second game. Though we never see it, even ATTON seems to accept it.
Lorenzo Belli from Haunting Ground, who temporarily restores his youthful looks for the final battle. Apparently, to quite a few fans, his newfound appearance was hot enough that they were almost willing to overlook the Squickiness of him going after his granddaughter, Fiona.
Mother Pearl, matriarch of the Boomers in Fallout: New Vegas, is a wise old lady who understands the need to break out of their reclusiveness just a little. Once you drag that old B-29 out of Lake Mead, Loyal (the Boomers' master technologist who's just as old as Pearl) demonstrates that he apparently has excellent knowledge the shape of Pearl's former figure by adorning the restored plane with nose art depicting her from way back when.
Oshare Bones from Puyo Puyo claims this about himself a few times throughout his story in Puyo Puyo! 15th Anniversary, although the player never gets to see what he looked like before his death. He claims to have had beautiful long, curly blond hair, but he threw all of his pictures of himself into the ocean and begs them to be left alone, claiming that they would bring back painful memories.
Halo's Dr Halsey was apparently quite good looking when she was young. Case in point, it's said that Cortana's appearance was based on that of her as a young woman.
"I hear Oak's taken a lot of interest in you, child. That old duff was once tough and handsome. But that was decades ago. He's a shadow of his former self."
Wendy Oldbag of Phoenix Wright: Ace Attorney claims in the first game that she was a mildly successful film actress in her youth. She also has a tendency to use Puppy-Dog Eyes an awful lot, implying there was a time in her life when that maneuver was actually effective.
In one (rather strange, even by Ace Attorney Standards) commissioned side-story involving the ghost of Wendy's Identical Grandmother and said grandmother's lover (very, very long story) proves that Wendy was right about being attractive.
Higurashi: When They Cry reveals that Shion and Mion's grandmother was rather attractive in one of the anime-only omakes much to Mion's surprise.
In Umineko: When They Cry it's occasionally noted, and later outright confirmed, that crazy old grandpa Kinzo used to look a hell of a lot like his bishonen grandson Battler when he was young. The manga also reveals that Kinzo's Old Retainer Genji wasn't bad-looking in his youth either.
From me The Bandit there's Bruno's mother, Eunyce, who - in several flashbacks - is seen in her past identity: Eunyce, Warrior Hottie! Sadly, she still wears her old, Stripperific costume waaaaay too often.
Ménage à 3 - In this strip, landlady Eulice Deville claims to have been beautiful when young. However, this claim is unconfirmed.
In The Order of the Stick, Roy meets his mother in the afterlife. Since in the Stickverse's good-aligned heaven you look like your own idealized version of yourself, she appears as the very attractive nineteen-year-old woman she once was, to Roy's Oedipal chagrin.
Sara: Roy, it's me, your mother!
Roy: Uh, sorry, no. My mother has a grey bun hairdo and osteoporosis, not pigtails and a rack.
Roy's dad shows him a picture of mum in a bikini.
Eugene: And can you blame me? Look at the rack on that girl!
Roy: Gah! Never show me mom like that again!
Subverted in the seriously NSFW comic Oglaf, when Ponce De Leon thought he found the fountain of youth after his old assistant became young and beautiful. But then she explains that she wasn't that beautiful when she was young. Too late; he then discovers he found the Fountain of Girl.
How I Killed Your Master starts off with the apprentice searching for the eponymous evil master's killer, who is the narrator and central hero of the story, who is an old man. Cut later in the story to when he was 10 years old, and then later when he's in his 20s. We also got a look at the Five Dragons when Master Fei unveiled the truth about Wong's father, and apparently Fei had quite a head of hair way back when.
Elanor of Kevin & Kell was one back in the day, so much that a picture of her from her younger days got leaked onto the internet (by her son Ralph, who didn't recognize her at all. His head literally imploded when he found out). Her son-in-law Kevin, though, believes she still is. He did recognize her, after all.
Pictured above: Avatar: The Last Airbender: Ty Lee sees a picture of two young women and ask who it is. Turns out it's the Creepy Twins Lo and Li, who then make the same pose as in the picture and almost make Zuko vomit.
In fact, this was implied in The Emperor's New Groove! It was a plot point in its previous version of Kingdom In The Sun and the series just recycled that.
In Recess, Spinelli discovers a photo that shows that Miss Finster was quite the looker when she and Spinelli's grandmother were entertaining the troops in the Pacific. In the film based on the series, we see flashbacks from the teachers. Miss Finster might have looked better when she was younger, but she still had the exact same raspy voice.
There was an episode of Rocko's Modern Life that did this with all the elderly people (or, technically, animals, since it is Rocko's Modern Life and all) in the vicinity. Rocko and Heffer were on a cruise in The Bermuda Triangle with Heffer's grandpa (among other old people), and this gigantic clock came along and completely switched around everyone's ages—the youngsters (Rocko and Heffer) were now old geezers and the old people (Grandpa Wolfe, et al.) were all young again. After all, it was the Bermuda Triangle and strange, unexplainable things were bound to occur.
A couple of episodes feature Ed Bighead like this, in one he was tall, handsome, and muscular and had a buzz cut before he became old, and another features him looking like a green skinned Lex Luthor before Heffer while working as a paper boy hit him with a newspaper that caused him to fall into a blender destroying his face.
Archie's Weird Mysteries has this happen to Miss Grundy in the episode "Twisted Youth", when the adults of Riverdale are reverted to teenagers. She spends most of the episode agressively pursuing Reggie, who's about to give in and kiss her when the effect's reversed.
Nerissa and Yan Lin in W.I.T.C.H. were very attractive once they reverted to their teenage guardian forms.
Animaniacs Slappy Squirrel was good looking in her younger years. See "Milk - It Does A Body Good" parody, where we see Slappy mature from babyhood to her current state in seconds. For one brief, shining moment, she's a veritable Jessica Rabbit (Jessica Squirrel), but only for the blink of an eye.
An episode of Scooby-Doo revealed that the grouchy old waitress used to be a water skiing champion who looked cute in a bikini.