I recently saw the movie ‘In Time’ (The 37% it got on Rotten Tomatoes seems a bit generous 
)Not really a spoiler since it was in every single trailer for the movie 'but -
Everyone stops aging at 25 years old, there where several characters who where supposed to be much older but looked 25. I don’t feel like the actors did a great job portraying an old person in a young body.
So, does anyone have any examples of a movie where old person in a young body was portrayed well?
The first movie that comes to my mind is “Big”. I’m pretty sure I’ve heard criticism of it here, but I thought it was absolutely charming.
Not a movie, but the latest incarnation of Doctor Who, Matt Smith, does a terrific job of playing what is essentially a young man trapped in an old man’s body trapped in a young man’s body.
I think the only criticism is that that’s a young person in an older person’s body. Acting childlike is relatively easy for an actor, but acting older is rarely done well.
I’d toss out The Tin Drum for consideration. Until now I hadn’t really thought about the fact that they had to film it with an actual child. (Granted there are a few cheats about it, but it’s done smoothly).
It’s been a long time since I saw it, but I remember Kirsten Dunst being wonderful in Interview with a Vampire. She gets vampirised when she’s maybe eleven years old - she stops developing physically, but keeps growing up in many ways mentally and emotionally, and she’s not one bit happy about how she’s ended up. Very well acted, and quite eerie.
Not a movie, but Tommy Solomon on 3rd Rock From The Sun, was the oldest of the aliens but trapped in a teenager’s body. Joseph Gordon-Levett played him quite well from the beginning.
I thought Zach Efron did a decent job in 17 Again playing someone who’s Matthew Perry’s age. Kind of a throwaway movie but I liked his performance.
In the movie “18 again”, Charlie Schlatter did a very good job of pretending to be George Burns.
::searches IMDB for “19 again”::
Citizen Kane comes to mind.
18 Again. That kid really does a good job. The best I’ve seen.
Let Me In. 12-year-old girl playing a 1000-year-old vampire. She does a pretty good job of it.
I second the naming of Kirsten Dunst in Interview With A Vampire.
How about Homer, the cranky-ass vampire stuck in a 13 year old body, in the criminally-unappreciated Near Dark?
Bowties are cool.
Nitpick…
A deleted scene from Let Me In establishes that Abby is only a little over 100.
In Freaky Friday Lindsey Lohan, of all people, did a good job of portraying a forty-year-old in a teen body.
I remember liking Vice Versa with Judge Reinhold and Fred Savage much more than Big. I haven’t seen it since the 80’s though.
I thought River Phoenix did a fantastic Harrison Ford impression at the beginning of Indiana Jones and the Last Crusade.
Ah interesting - of course I just made up the age since it was never mentioned in the film proper; I remember her saying only that she was in fact “very old”.
The was an episode of Highlander with an old immortal with a young teenage body pretending to be an innocent. He played it well.