Due to Double Standards concerning age and perceived attractiveness, adult male characters are usually played by actors of about the character's age, but female characters of middle age and older are often played by actresses noticeably younger than the character should be. This becomes jarring when a character's mother, or a woman otherwise stated to be of an older generation, is played by someone only slightly older or, in some cases, younger than him.
Named for Hamlet, Prince of Denmark's mother Gertrude, who has traditionally been played by improbably young actresses (it's less common in more recent productions). This is most prominently and ridiculously pronounced in Laurence Olivier's film version of Hamlet, which featured Eileen Herlie in the role of Gertrude despite the fact that she was eleven years younger than Olivier himself.
A related effect tends to crop up in animated portrayals of middle-aged women. If a female character has an obviously attractive mother, expect both of them to look about the same age. That being said, male examples, though uncommon, do exist.
Sometimes this trope can be forced by a movie that covers a long period of time. If we see the mother of a small child, and then see the child grow to adulthood, it's usually easier to cast a young woman as the mother and "age" her with makeup, if at all, instead of the other way around. Some actors can be Younger Than They Look and get cast as roles that are older than they are - Jon Hamm, for instance, talks about being twenty-five and auditioning to play fathers on Teen Dramas.
Appears quite often in voice acting too, since looks, of course, don't matter. Due to Vocal Dissonance, some voice actors can sound much older than they are (or younger). As rather a lot of animated children are voiced by adults with high-pitched voices, it's not uncommon for the actors to be the same age or even younger than those voicing their children.
Closely related to Hollywood Homely and a side effect of Underage Casting. This is one way to invert Dawson Casting and is frequently a side effect of it (having a forty-year-old actress playing the mother of a teenager is perfectly plausible, but when the actor playing the teenager is 25, it becomes a problem.) Often overlaps with Hollywood Old, since it's usually impossible for a Hollywood Old character to have a teenage or adult child without their (lack of) age difference becoming a Playing Gertrude. However, when both actors are middle-aged or older, it's easy to have a Playing Gertrude without either character being Hollywood Old. Contrast Age Lift, where the role is changed to make the actor age-appropriate for the role. See also Absurdly Youthful Mother, where a parent is or appears unusually young in-story, as well as Mum Looks Like a Sister, where parent and child (typically mother and daughter) look like siblings instead.
- Tekken Movie 2010: Asuka's Revenge is, as the name suggests, a rewrite of the 2010 live-action Tekken movie with Asuka as the main character. The author even provides a "cast list" with characters that were in the actual movie being played by the same actors and the author providing casting for anyone who wasn't. His choice of actress to play Michelle Chang is actually three years younger than the one playing her adopted daughter Julia (canonically nearly 20 years Michelle's junior). Overlaps with Dawson Casting as both actresses are closer to Michelle's age than to Julia's.
- Strange Magic: Maya Rudolph is seven years younger than Alan Cumming who plays her character's son.
- The film Lego DC Comics Super Heroes Justice League: Gotham City Breakout" has Commissioner Gordon voiced by Eric Bauza, who was born in 1979. Outside of Greg Cipes (1980) as Beast Boy and Sarah Hyland (1991) as Batgirl, he's younger than the rest of the cast despite his character being older.
- Batman Unlimited: Monster Mayhem sees Khary Payton reprise his Teen Titans role as Cyborg, while his father Silas Stone is voiced by Cedric Yarborough, who's 1 year younger.
- The Book of Life has Manolo's grandmother voiced by Grey Delisle, who was 41 years old when the movie was released. Her character's son, Carlos Sanchez, is voiced by Hector Elizondo, who was almost 78 when the movie came out.
- My Little Pony: The Movie (2017) has Uzo Aduba (who was born in 1981) as Queen Novo and Kristin Chenoweth (who was born in 1968) as her daughter Princess Skystar.
- The second Curious George movie, Curious George 2: Follow That Monkey, has Mr. Bloomsbury voiced by Fred Tatasciore while Jeff Bennett voices Ted, one of his employees. Even though Tatasciore's character is older than Bennett's character, the former is five years younger than the latter.
- Justice League: Doom sees Robin Atkin Downes (born in 1976) voice Alfred, a character nearly twice his age. Additionally, he's younger than Kevin Conroy (born in 1955), who reprises his role as Batman (though Batman himself is around his 30s as always).
- Batman: Return of the Caped Crusaders and Batman vs. Two-Face, both of which are animated adaptations of the 1966 Batman television series produced 50 years later, sees Jim Ward (1959) as James Gordon, Lynn Marie Stewart (1946) as Aunt Harriet, Steven Weber (1969) as Alfred, and Thomas Lennon (1970) as Chief O'Hara, with all of them being considerably younger than Adam West (1928) as Batman and Burt Ward (1945) as Robin even though their characters are older.
- In Moana, Gramma Tala is voiced by Rachel House, who was only 45 at the time of the movie's release. Temuera Morrison, who plays her son, is nearly eleven years older than she is.
- In Frozen, Elsa and Anna's mother Queen Iduna's single line was voiced by co-director Jennifer Lee, who is 5 months younger than Idina Menzel and 11 years older than Kristen Bell. The gap becomes much larger in the 2019 sequel Frozen II where Iduna is voiced by Evan Rachel Wood, who is 32, seven years younger than Kristen Bell and 16 years younger than Idina Menzel.
- The Lorax: Jenny Slate, who voices Ted Wiggins' mother, is actually only five years older than Zac Efron.
- Ice Age 4: Continental Drift: Wanda Sykes voices Sid's senile granny. In reality, John Leguizamo and Sykes were born in the exact same year of 1964, just about three months apart.
- While unlike in Gotham, the Saran Essen of the comics is younger than Jim Gordon, she's still older than Bruce. In Batman: Year One, Katee Sackhoff voices Essen — and is two years younger than Benjamin McKenzie, who voices Batman.
- Batman: Gotham by Gaslight sees Tara Strong and Grey DeLisle, both born in 1973, respectively voice Marlene Mahoney and Leslie Thompkins, who are in their 60s. For further reference, they're both younger than Bruce Greenwood, who in a bit of Dawson Casting is once again Batman.
- Justice League: The Flashpoint Paradox sees Grey DeLisle voice the middled-aged Nora Allen and Kevin McKidd voice the Batman of the Flashpoint Universe, a senior citizen, and both actors were born in 1973. DeLisle is three years younger than Justin Chambers (born in 1970), who voices Barry, and McKidd is almost two decades younger than Kevin Conroy, who reprises the role of Batman. Likewise, Danny Huston, born in 1962, voiced the also senior citizen Sam Lane, while not stated on-screen, the father of Lois Lane, who was reprised by Dana Delany, who was born in 1956.
- In Mark Schultz's Letters from War, the woman playing the soldier's mother looks like she's only as old as he is.
- In the Strauss opera Salome, which sets the Biblical story to music, there is often an interesting aversion in which the soloist playing Salome is often far older than the soloist playing Herodias, her mother. This is probably because Salome is a central role and Herodias is at most a bit-part: older opera singers tend to have the prestige and clout that gets them the starring roles, and newbies are relegated to bit-parts. Therefore, as noted in the BBC production of Salome, we get the incongruity of a fifty-year-old daughter dancing a salacious striptease in front of her enthralled stepfather and twenty-something mother...
- Probable in any ballet, especially with those with mothers and parents in small non-dancing roles, such as The Sleeping Beauty, Romeo and Juliet, Giselle, or Swan Lake, given a) a ballet dancer's short performing lifespan of 18ish-35ish mean that even the most mature ballet dancers aren't way older than the younger ones and b) most mature ballet dancers are principals and will only dance in principal roles. It wouldn't be out of place to have a thirty-two-year-old principal play sixteen-year-old Aurora, and a twenty-year-old soloist play her mother.
- Justified in any production of Gilbert and Sullivan's Iolanthe. The mother and aunts of the male lead are supposed to all look noticeably younger than him, and one of the jokes is the need for him to explain to people (such as his intended bride) why teenage girls are seen hugging and kissing him. (There is a good reason for the apparent age difference.)
- Inverted in-story in The Grand Duke when mention is made of an actor who refuses to play Romeo unless his grandmother plays Juliet.
- King Lear is as often as not played by a younger man due to the intense physical nature of the role in most productions. Whether this trope comes into play or not differs depending on the quality of the given Lear's age makeup (most major productions are pretty well done, and the role is pretty much always played by mature actors — it's just that the text establishes that Lear is over eighty years old).
- In the musical of Spring Awakening all of the adult female roles (including several teenage characters' mothers) are played by one woman. In the original production, the understudy for this role was 30-year-old Frances Mercanti-Anthony. This makes her a bit young for her motherly roles to begin with but combined with Dawson Casting of a few of her "children" (such as 20-year-old Lea Michele as the daughter of one of her characters) the age gap was even smaller.
- Pretty much inevitable in high school and college theater, since all the actors will be about the same age.
- In the early installments of the Myst series, Rand Miller streaked his hair and beard grey and affected a gravelly, world-weary tone of voice to play the much older Atrus; it also helped to differentiate Atrus from his son Achenar, whose hair was darker and who spoke in a higher register. By the time of Exile and Revelation, Rand was old enough to play Atrus with his natural voice and without fake grey in his hair; casting a different actor as Achenar in Revelation also helped. The fact that Atrus has more long-lived D'ni blood than his sons might help account for Rand looking awfully young to be Achenar's father in-Verse.
- Lia Montelogo was only 19 when she did the photoshoot for Sindel in Mortal Kombat 3. She was actually a few years younger than Becky Gable, who plays Sindel's daughter Kitana in the upgraded version of the game, Ultimate Mortal Kombat 3. This is due to the fact that the two characters are part of a fictional humanoid race known as Edenians, who age much slower than Earthrealmers.
- The cast of Noob consists of people of similar age, and the "X is Y's parent" twist has happened a couple of times. In both cases, the parent does not look old enough to have an adult child (the youngest characters were in their late teens in Season 1). The cartoony art style of the Comic-Book Adaptation doesn't help much in this regard either. In addition to this, the actor playing Abraham, introduced as Sparadrap's father from the start, is actually a few years younger than the actor playing Sparadrap.
- RedLetterMedia videos frequently features the character of Mr Plinkett, an elderly man who is performed by Rich Evans in Half in the Bag and Mike Stoklasa in the Mr. Plinkett Reviews, both men in their 30s and 40s.
- Kevin Conroy wasn't even in his 50s yet when he voiced old Bruce Wayne in Batman Beyond (who was about eighty years old during the series proper, and nearing the century mark in the Fully Absorbed Finale episode of Justice League). Similarly, Angie Harmon wasn't even 30 yet when she took over from Stockard Channing in the role of the older Barbara Gordon (who's in her 60s) in Return of the Joker and Season 3 of the series proper.
- Gravity Falls creator Alex Hirsch voices Great Uncle "Grunkle" Stan Pines, Old Man McGucket, and Gravity Falls' 100+-year-old mayor. Hirsch himself was in his late 20s during the production of the series.
- Same for his friend Justin Roiland, who voiced both title characters on Rick and Morty, the former being around eighty despite being only being his mid-30s making him only slightly younger than Sarah Chalke, who plays his daughter, and barely older than Spencer Grammar, who voices his granddaughter.
- April Winchell was in her late 30s/early 40s when she voiced sexagenarian Miss Finster on Recess.
- Sherri Stoner was only in her 30s when she voiced Slappy Squirrel on Animaniacs, who is stated on the show to be an octogenarian.
- Marvel's Spider-Man sees Ben Diskin, a man in his mid-30s, voice the middle-aged Spencer Smythe. Furthermore, Ben Diskin is 9 years younger than Jason Spisak, who voices Spencer's more famous son, Alistair.
- DuckTales (2017) sees David Tennant as Scrooge McDuck. Scrooge is an old man and Tennant is in his 40s. Additionally, Toks Olagundoye, who's in her 40s, voices the also older Ms. Beakley and Beck Bennett, who voices Launchpad, is younger than the voice actors for Huey, Dewey, Louie, and Webby despite the character being older (and Bennett being 3 when the original series first aired).
- On Elena of Avalor, King Verrago is the father of Skylar, even though the former is voiced by Andre Soliguizzo (who was born in 1966) and the latter is voiced by Carlos Alazraqui (who was born in 1962).
- In one episode of Be Cool, Scooby-Doo!, Shaggy's grandmother is voiced by the same voice actress as Daphne (Grey Delisle) even though Matthew Lillard (Shaggy's voice actor) is 3 years older than Grey.
- Muppet Babies (2018) has Nanny, voiced by Jenny Slate, who's younger than all the voice actors for the title characters, save for is Ben Diskin (voice of Gonzo), who is only months younger than her. Likewise, Statler and Waldorf, who are old men, are voiced by Eric Bauza and Matt Danner, who are in their late 30s.
- DC Super Hero Girls has Granny Goodness voiced by 48-year-old April Stewart.
- Samurai Jack has Ashi voiced by Tara Strong while her mother is voiced by Grey DeLisle, who's 6 months younger than her.
- Artemis Pebdani, who voices Alice Green on Big City Greens, was born in 1977, making her younger than Bob Joles (voice of Bill, born 1959) and Wendi Mc Lendon Covey (voice of Nancy, born in 1969).
- In The Perils of Penelope Pitstop, the title character was voiced by Janet Waldo, while her ward Sylvester Sneekly (alias The Hooded Claw) was voiced by Paul Lynde. Waldo was actually six years older than Lynde.
- In Phineas and Ferb, the main group of kids have ages 15 or under, according to the creators (with Candace being 15). None of their voice actors have ages falling into that range, with one of them, Maulik Pancholy, voice of Baljeet, being in his late thirties (Pancholy was born in 1974). Incredibly, he's not even the oldest - the winner of that particular honor is Kelly Hu, who was 39 when she began voicing Stacy (Hu was born in 1968)!
- Jeremy and Vanessa were roughly the same age as their voice actors, Mitchel Musso and Olivia Olsen, respectively, during the casting. Even so, however, both Musso (b. 1991) and Olsen (b. 1992) are actually younger than Thomas Sangster (b. 1990), the voice of Ferb, a preteen.
- Bob's Burgers has the eldest of the Belcher children, Tina, voiced by Dan Mintz, who is actually the youngest of the main cast (Mintz was born in 1981). Eugene Mirman (middle child Gene) and Kristen Schaal (youngest child Louise) are both older than Mintz (they were born in 1974 and 1978, respectively).
- In The Loud House, born in 1971, Brian Stepanek, Mr. Loud's voice actor, is actually younger than some of Mr. Loud's daughters' voice actresses, such as Lara Jill Miller (Lisa), Nika Futterman (Luna) and Cristina Pucelli (Luan), who were born in 1967, 1969 and 1970, respectively.
- Similarly, in the spinoff The Casagrandes, Angelica Aragon (born 1953), who voices Mama Lupe, is younger than Sonia Manzano (born 1950), who voices Lupe's daughter Abuela Rosa.
- Dinosaur Train has The Conductor voiced by Ian James Corlett (born in 1962) while his mother is voiced by Tabitha St. Germain (born in 1976) .