For the sake of this thread, I’d like to exclude movies/TV in which the same actor was playing him/herself in flashback/flashforward. Rather, that the character’s age was much younger/older than the actor playing it but you were expected to believe it.
For example: In The Birdcage, Calista Flockhart was playing a 17 year old, when at the time she was 32.
Or in the original Manchurian Candidate, where Angela Landsbury was playing Laurence Harvey’s mother, when in fact she was only three years older than Harvey. So, she was playing a woman old enough to have a 33 year old son at the age of 36.
I know I’m forgetting some rather obvious ones with a larger age gap than my examples, so I put it to the Dopers.
There are cases (in fantasy & sci fi) where characters are hundreds or thousands of years old, so that trivially the actors are a lot younger than their character, so I suspect you might want limit to realistic movies/programs.
Estelle Getty was 62 when she started playing the role of Sophia on The Golden Girls. Sophia was 80 when the series began. (18 year difference)
Shirley Henderson was 39 for HP:Goblet of Fire portraying Moaning Myrtle, who would have been no older then 17. (somewhere between 22 and 26 year difference)
Although I love the movie, I think that 41-year-old Laurence Olivier was a bit long in the tooth for the 1948 film version of Hamlet. Although Hamlet’s age is not given, he’s supposed to be a university student. Eileen Herlie, who played Gertrude, was, in real life, 13 years younger than Olivier.
Isabel Sanford was twenty years older than Sherman Hemsley, so assuming that most married couples are expected to be around the same age (there are indications in the show that George was slightly older than Weezie), she was around twenty years older than the character she played on The Jeffersons.
Jessie Royce Landis played Cary Grant’s mother in North By Northwest despite only being seven years older than Grant. Grant at the time was 54, though he was playing the part younger – though never mentioned, I would doubt he was supposed to be much over 40.
41 year old Cicely Tyson played a centennarian in The Autobiography of Miss Jane Pittman.
That may not count under the no-flashbook rule, but she spent a considerable amount of time as her old-age character.
Hal Holbrook first did his one-man show Mark Twain Tonight! when Holbrook was 29. Twain’s age isn’t precisely noted in the show, but Twain died at age 76 and Holbrook’s makeup was obviously modeled on photos of Twain in his later years.
Sigh. OK, I’m obviously talking about actors playing characters whose age they’re supposed to be expected to represent in normal reality, not John DeLancie playing 200 billion year old Q, or David Tennant playing a 900 year old, or the baby from Ten Commandments playing Jesus, or Al Pacino as the Devil, or anything else along those lines.
And to clarify the flashback/flashforward rule mentioned in the OP, yes that includes wearing obvious makeup to appear older. If a young actor played someone older, they had to look like they normally did, and vice-versa, with minimal effort to wardrobe / hairstyling.
I’m not even looking for the most convincing portrayal, just the biggest difference. I imagine some terrible 50’s B-movie with middle aged men posing as teenagers would be the winner.