Ignoring fantasy characters, I’d suggest 33 year old Dustin Hoffman playing 121 year old Jack Crabb in Little Big Man.
Just the other day I clicked past Grease, where Stockard Channing, at 34, played 17 year old Rizzo - so not 25 years, but double the age.
That’s going to be tough to beat for realistic human ages.
The Man Who Shot Liberty Valance has 50 year old actor O.Z. Whitehead playing a teenager, as he’s introduced with a man scolding him for cutting school to go fishing.
What about Robin Williams, who was 45 in 1996, playing a 10 year old in Jack?
A slightly smaller age gap: 44 year old Martin Short playing a 10 year old in the 1994 movie Clifford?
Brad Pitt in, “The Curious Case of Benjamin Button”.
Yeah, probably lots of good examples if you count animation, which you probably shouldn’t.
Lots of examples from sketch comedy, too, like (from SNL) Amy Poehler’s Kaitlin or Gilda Radner’s Judy Miller.
Probably some good examples of characters who aged over the course of a movie, portrayed by the same actor over the course of the movie (e.g. Tom Hanks would have been in his late 30s when Forrest Gump was filmed).
Not a huge age gap, but my favorite example. In A Hard Day’s Night Paul’s Grandfather, who apparently is in his mid to late 70’s (?), was portrayed by 52-years old Wilfred Brambell.
That’s what very clean living will do for you…
Laurel and Hardy as their sons.
I don’t think it makes much sense to include supernatural characters. It’s not like there are a lot of age appropriate actors to play a 6500 year old.
The characters in ‘The Munsters’?
If we do include animation voice actors, then June Foray deserves a mention, having played Granny from age 38 to 97. No matter what age you assume Granny was, there’s a big age difference in there somewhere.
Richard Chamberlain was 49 when The Thorn Birds premiered, and his character was supposed to be in his mid-20s, I believe.
He was very clean.
Okay, how about Jonathan Winters as Merth on Mork and Mindy?
Wilford Brimley has only 50 when Cocoon was filmed!
Kathleen Turner played a 17-year-old in Peggy Sue Got Married when she was 32. It actually worked, sine Turner used her expression to switch between ages.