Joseph: That's a picture. Of me. Sitting on a couch. With my legs spread open. Naked. This picture was on the cover of GDILFs Magazine's 'Top Ten Sexiest, Most F*** able Grandpas'. I was number one. Beating both Monkey D. Garp from One Piece, and Uncle Iroh from Avatar.
D'Arby: How...recent...is that picture?
In-universe it's mentioned repeatedly that's he's very attractive even in his old age. To the point that the protagonist of the fourth part is his bastard son. Who was conceived when he was 65, after his grandson Jotaro had already been born.
Even taking into account the time he got de-aged by a Reality Warper, Magneto is decidedly not a young man. He was born in the late 1920s, and Comic Book Time doesn't change this since being a Holocaust survivor is central to his character. Chronologically he's in his late 80s, and biologically he's probably in his late 50s or so. Despite this, he's a buff, attractive-looking man whose only real hint at not being young is his white hair...except that it has been white his entire life so that's a false hint.
Since Judge Dredd's timeline progresses at a 1:1 rate with real time, Psi Judge Anderson has been a street judge for at least 35 years, placing her in her early 50's. As a Psi Judge, she doesn't take the age-slowing drugs available to regular Judges and is still consistently depicted as a very attractive woman who is frequently hit on by men half her age.
In the Empath: The Luckiest Smurf story "Empath's Wedding", Flowerbell the woodnymph still comments on Papa Smurf's looks like this.
Sisterhood Series by Fern Michaels: Myra Rutledge and Countess Anne "Annie" Ryland de Silva. Both of them are in their 60s and heading on to 70s. Make no mistake, they are old enough to be your grandmother, and they are incredibly sexy! In fact, Weekend Warriors has Nikki Quinn and Barbara Rutledge commenting that Myra looks better at 60 plus years old than they do at 30 plus years old. Now that's hotness!
Belgarath in The Belgariad is an Elderly Immortal who looks to be in his eighties or nineties. Right up until he takes off his shirt, demonstrating that while his face may be that of an old man, his body is not.
Kinsey Millhone definitely thinks her landlord Henry, who is around eighty, is very sexy.
Lady Abigail Irene Garrett in Amsterdam is around 50 when we meet her, and is definitely still a sexually vibrant woman.
Paul Lassiter's mother in Spin City. Paul is baffled by all the attention she gets until the other guys point out her sexiness, causing Paul to give her the head to toe. "OH MY GOD! I just checked out my own mother!" "And?" "She's a FREAKING HOTTIE!"
Scrubs: JD has sex with a new grandmother (her daughter was a patient, for the delivery), who easily fits the category in "My Best Moment".
Gemma from Sons of Anarchy, enough to be checked out and commented on by the much younger Prospect, Half-Sack.
Bree van de Kamp from in Desperate Housewives is coming from the attractive mother territory to this one. Reinforced and lampshaded, in both ways, when, at the same time, she begins her menopause (the grandma side) and gets involved with the handsome, well-build and 15 years younger Keith (the hot side).
Dr. Quinn, Medicine Woman: Dorothy was an older and very attractive woman, estranged from her abusive husband and later widowed. She's courted by her brother-in-law Loren Bray and much younger man Jake Slicker, who initiated their May-December Romance. Dorothy's old age is marked when she thinks she's pregnant but she's in fact beginning menopause.
30 Rock made reference to Helen Mirren in a bikini, prompting Liz to say "It's not possible, what is she, a wizard?"
My Grandmother's Ravioli: due to the nature of the show, Mo Rocca finds himself meeting with a veritable full spectrum of grandmothers, ranging from the matronly to the lovely. But one particular episode stands out. It turns out that the grandmother in question started her family young, and her children did as well. Which makes her technically a grandmother at the age of 52, and still stunning at that.
Fiona Goode from American Horror Story: Coven (played by 64-year-old Jessica Lange) is considered quite attractive and is stated to be quite beautiful in her first scene. However, she isn't satisfied with being this trope and tries desperately to become younger and immortal.
In Dragon Age II, Flemeth drops the ragged old lady look that Morrigan and the Warden know her by and instead wears figure-clinging armor, has white horned hair and a generally cleaned-up face. As seen here.◊