Laurence Harvey - 34, Angela Lansbury — 37
“The Manchurian Candidate” (1962)
Dustin Hoffman — 27, Anne Bancroft — 33
“The Graduate” (1967)
Robin Williams — 30, Glenn Close — 35
“The World According To Garp” (1982)
Colin Farrell — 28, Angelina Jolie — 29
“Alexander” (2004)

If
you don’t understand the numbers above, that’s because they don’t make
any sense. The numbers attached to the actors are their reported ages
at the time the films were released which starred the actresses listed
beneath them, with their respective ages, as their characters’ mothers
(or, in the case of “The Graduate”, mother-in-law).
Now, even allowing that some actresses are sexually precocious, this does seem a bit ridiculous, no?
What’s behind it?
The most obvious cause of course is that Hollywood casting brings
together the industry’s sexism with its ageism. Whoopi Goldberg’s joke
about how on Oscar night the producers get so drunk that they sleep
with women their own age isn’t really a jest. The casting in these
movies may have seemed perfectly reasonable to the films’ male bosses.
“Garp” director George Roy Hill was no spring chicken and notorious
casting couch auditioner Oliver Stone is rarely confused with Doogie
Howser.
To this factor also add the usual Hollywood cynicism about the
relationship between sex and box office receipts. Lotus-land logic
holds that all commercial movies are love stories with beautiful
people. So, if there isn’t a story to be found in the script with young
lovers, the thinking goes, make the mother into the young lover. What’s
wrong with hinting at incestuous desires? This reasoning has been
around at least since early MGM head Irving Thalberg was around, if his
sometime scenarist “Gentlemen Prefer Blondes” author Anita Loos can be
believed.
All of these films intimated (or more than that) at a “romance of the
family”, and all save the last prospered at the box office.
And there’s something else that may be less obvious. Many older female
stars are so vain that they refuse roles that call for them to play
mothers. (“How could anyone believe that I would have an adult child?”)
Doris Day and Jeanne Moreau both turned down the role of Mrs. Robinson,
in part because they thought they were too young for it.
Whatever the reasons are for this practice, it isn’t good. It’s not
only that it looks strange on screen. It’s also that it not so subtly
sends more mature American women the message that if they don’t look
young they don’t really matter.
Reader Comments (1)
But much more common were variations on the set-up in, for example, "The Bachelor and the Bobby-Soxer", with Cary Grant and a teenage Shirley Temple, with Temple having a crush on Grant (though who doesn't really). The mother role in the film is actually Temple's character's older sister, who doubles as Grant's romantic interest.
A more complex example of the same dynamic is "The Major and the Minor", in which Ginger Rogers pretends to be a child in order to get cheaper train fare. She ends up in an initally unconsummated romantic relationship with Ray Milland, playing the evidently myopic Maj. Philip Kirby. Rogers becomes embroiled in competition with the Major's fiancé, who is in all practical senses the mother of her younger sister, who Rogers befriends.
The hot mom has been around since the beginning of cinema, but to get around the age problem Leaf deals with, and the social taboo of the sexual mom, the mom has been disguised as the older, maternal sister. To bring it around to Leaf's incest theme, we'll close with everyone's favorite line in "Chinatown" -- "Mother... Sister... Mother... Sister... Mother Sister."