Cool, I couldn’t remember. Still quite a disconnect.
Yeah, it doesn’t make much difference. It was just my geeky nitpickery coming out.
Sarah Bernhardt was officially 70* and still performing on stage as 13-year-old Juliet.
*Her birth records were apparently destroyed in a fire, so she may have fudged the numbers a bit when she forged some new ones.
How old is Connor MacLeoud supposed to be? 
Marvin the Paranoid Android is 37 times older than The Universe itself. (HHGttG) So, Stephen Moore or David Learner have a pretty good claim.
Ford did this sort of thing more than once. In The Man Who Shot Liberty Valence, John Wayne and James Stewart, both in their mid fifties, play characters in their early twenties. Conversely, 12 year old Roddy McDowall plays a character who ages to his early twenties in How Green Was My Valley.
Speaking of John Wayne, it’s not clear exactly how old the brothers are meant to be, but in The Sons Of Katie Elder, there’s a 36 year age gap between Wayne and the man who plays his youngest brother, and it’s obvious in the story that the gap should be nowhere near that large.
In none of these cases does it harm the film, though, and in How Green Was My Valley it actively improves it, adding to the dreamlike, surreal quality of an old man’s memories of childhood and early adulthood.
I recall Rob Reiner had a short-lived 1978 TV series in which he did a Dustin Hoffman a la Little Big Man. He was 31 years old, but his character was 89. He would appear at the beginning in the “present day” (1978) and reminisce about events in the early 1900s, and those events would then be portrayed. Free Country was the show. It was pretty good, and I was disappointed when it got pulled.
I don’t know how old the television Margaery Tyrell is supposed to be (I’d guess 22-23), but book-Margaery is 16 when she’s introduced.
Natalie Dormer. the TV actress portraying her is 32
Roughly a 25-year spread, plus or minus a few years.
A good 20 years in your estimation.
Without any plot trickery, Joan Allen’s Morgause had a 31-year spread. The winner?
Well, if we aren’t excluding supernatural/alien/immortal/whatever characters as a special case, Sarek was stated to be 102 in his Original Series appearance as is of course correspondingly older when he shows up in The Next Generation.
Also 102 is Maester Aemon in Game of Thrones, but the actor who plays him, Peter Vaughan is only … um … 91. Never mind.