Bea Arthur was a year older than Estelle Getty in “Golden Girls.”
Lionel Jeffries was a year younger than Dick Van Dyke in “Chitty Chitty Bang Bang.” (Not exactly a ‘mother,’ thought.)
The same was true on 8 Simple Rules. When the show started, seventeen year old Kaley Cuoco was playing the older sister of twenty-three year old Amy Davidson.
Taraji P. Henson, 7 years younger than Brad Pitt, played his mother in The Curious Case of Benjamin Button. Though the premise was indeed curious, it does technically meet the criteria of the OP’s question.
“Gone with the Wind” has Barbara O’Neil playing the mother Ellen O’Hara. She was 3 years older than Vivien Leigh, 6 years older than Evelyn Keyes and 7 years older than Ann Rutherford, her on-screen daughters. On the other hand Leslie Howard was 20 years older than Leigh and only a year younger than Thomas Mitchell.
Which is almost exactly not what the OP is asking about.
(Or, well, what I assume the OP is asking about. The “vice versa” certainly leaves it open to interpretation. But “actors who were older than the actors playing their parents” sure sounds like a more interesting list than the other way around.)
Kate Nelligan played Nick Nolte’s mother in The Prince of Tides, and she is nine years younger than he is. She played the role in age make-up, though, and also played the character in flashbacks without the age make-up, and with a child playing Nolte’s character, so that may not be exactly what the OP is looking for.
Examples where the parent actor was older, but not old enough to actually be the parent abound, especially on TV, where teen characters are “Dawson cast,” (played by actors over 18 who look younger, in order to be able to work as adults, and not require the short hours, and teachers on the set, and all that are required for actors under 18), but “parents,” and pretty much anyone over 25 is frequently younger than the character’s stated age, in order to assure that the character is going to age well.
If you want, not exactly a vice-versa, but just an odd situation, on One Day at a Time, both Mackenzie Phillips and Bonnie Franklin were younger than their stated ages-- Frankiln still wasn’t quite old enough to be Phillips mother, being about 15 years older than Phillips, but Phillips was about a year younger than the character she was playing, while Franklin was three years younger than her character. More interesting, in reverse Dawson casting, Valerie Bertinelli was only a few months younger than Phillips, but she her character was supposed to be almost two years younger. So, Bertinelli wasn’t really young enough to be Franklin’s daughter either. IMO, Bertinelli continues to look a few years younger than her actual age.
Not a film, but television. On the original 1960s version of The Forsyte Saga, Kenneth More, who played Young Jolyon, was 4 years older than the man who played Old Jolyon, his father.