Pretty much.
RE: the secession. Apparently that was a fact of another country that Shakespeare got right (probably because his source, IIRC Saxo Grammaticus, had it right); the Danish ruling party elected the king from a group of eligible people. I like to imagine a backstory where Gertrude was a queen regnant (like William I & Mary II) with Old Hamlet, and Claudius married her in order to become king.
They had another actress at the very beginning. Was she still just 14 when Goldberg stepped in?
Not the biggest gap, and it’s a bit unclear the intended age, but it appears that Maggie Grace plays a 16-year-old in the Taken franchise despite being around 30. I was thoroughly confused throughout much of Taken 2 because her just learning to drive was a significant plot point. Why didn’t she learn to drive 10 years ago?
Yeah, I’m seconding The Blob. Steve McQueen’s character was supposed to be a high school student.
ETA: According to IMDB, born in 1930, movie released in 1958. Well, I’ll be, that isn’t as big a gap as I had always thought…
Leaving out God or gods, whoever played Methuselah in the recent Noah movie will take some beating.
Not to mention Noah himself. But aging up characters with make-up is pretty common.
Ingrid Bergman played her Gaslight character very briefly as a child-- like a 10 or 11-year-old, and it’s very effective. It’s a Victorian period piece, so they have her dressed like a child with her hair down, and she gets into and over-sized cab (hansom cab), so she looks small, along with a couple of actors we see from the waist down, and she’s lit with a sort of odd glow, so we can’t see a lot of detail-- it’s maybe a one minute scene, if that, but she’s 28, and really looks like a little child.
That was a trick DW Griffith used a couple of times to get 5’4 Lillian Gish to look even smaller than she was when she played battered teen Lucy in Broken Blossoms– the other actors were tall, and the sets were a little out of perspective, plus, Griffith used forced perspective in a few shots to make Donald Crisp tower over Gish. Crisp was only about 5’9, but he looks huge in this movie. I think he might be in boots that add some height as well.
This doesn’t really count, but Jack Benny was probably still “39” when he died at age 80.
There’s a lot of fascinating scholarship about this (and I’m not sure that most scholars agree with the theory you mention). A few years ago an SDMB thread convinced me that Hamlet is supposed to be 16 - and that the gravedigger’s line is supposed to be “sixteen,” not “sexton.” To me there are some important aspects of the play that make much more sense if you believe Hamlet is that young, and I’d like to see an almost-age-appropriate Hamlet one day. But for the most part he and Romeo and Juliet and a lot of Shakespeare’s other young characters are going to continue to be played by older actors, both because they’re challenging roles that would be difficult for a very young actor and because audiences are used to pretending that 25- and 30-year-olds are teenagers.
John C. Reilly and Kristen Wiig play characters that age from 14 to 68 and 12 to 66, respectively, in “Walk Hard”. Reilly and Wiig were 40 and 32 at the time.
That reminds me of Howard Stern playing his college-age self in Private Parts when he was in his early 40s.
Yeah, but at least Howard and the filmmakers acknowledged this. As soon as the college scene starts Howard says on the voice over something like, “I know what you’re thinking, isn’t that guy a little old to be starting college!? But just go with it…” 
No, they weren’t, the characters are a good four or five years younger than the actors were when the show started.
In the 1948 Hamlet, Laurence Olivier was 41, Eileen Herlie, who played his mother Gertrude, was 30.
You sure about that? They were 13 and 14. Were the book characters really in the 8-10 range?
yes. Brand was 6.
Chris Evans is 32, but his Captain America character is 95. 
We were talking specifically about the girls.
At the beginning of the first novel, Sansa is 11 and Arya is 9.
Henry Fonda starred in the film version of “Mister Roberts” when he was about 50. One of the points mentioned in the film was he was a med student before enlisting.
From Wiki:
Fonda was not the original choice to star in the film version; Warner Bros. was considering William Holden or Marlon Brando for the lead role. The studio thought Fonda had been on stage and off the screen so long (8 years) that he was no longer a movie box office draw. In addition, when filming began he was 49, much older than the average lieutenant junior grade. Fonda was only hired because director John Ford insisted.
Mel Brooks was The 2000 Year Old Man.
I guess whoever played either Jesus or Satan in any movie/tv show, huh?
In the Tom Cruise / Brad Pitt / Christian Slater Interview With the Vampire movie, Kirsten Dunst as Claudia was 12. Her character (in the book) starts at age five and then is what, a couple of hundred when she dies?
I don’t think it was a couple hundred years. Louis’s story begins in 1791, so Claudia had to have been turned later than that by at least a few years, to give time for the early parts of the book to happen, and the events at the Theatre des Vampires can’t have occurred later than the late 1800s. At the outside edge, it was a little over a century.