Siblings tend to be relatively close in age. But there's a wide period where someone can become a parent, which can result in decades of difference in age. One sibling may be in diapers when the other is already at university or even has children of their own. They're practically in different generations despite being from the same generation. This could lead to Big Brother Instinct, and for a slightly shorter age gap, Annoying Younger Sibling.
More often this is because they're half-siblings, with the younger sibling being the result of a MayDecember Romance on their shared father's part. Or they're full-blooded siblings, but one was born early into their parents' relationship (likely a Teen Pregnancy) and the latter in their late 30s/40s, maybe even 50s with an Absurdly Elderly Mother. Or long after having their first kid, the parents chose to adopt (or vice versa; parents who are having trouble having kids might adopt a child then later succeed in giving birth).
Because of the large age gap, the siblings are likely to have an estranged relationship. If they're close, the older sibling may be more of a Parental Substitute or uncle/aunt in their behavior, rather than a regular sibling interaction. This can also lead to an uncle/aunt around the same age or even younger than their nephew/niece, who if close might share a sibling or cousin-like bond. Maybe they'll make jokes about the situation.
If one of the parents is immortal, this is almost guaranteed, though the age difference might be so huge the older sibling died long before the younger was even born. Producing these is semi-expected for kings and general nobility, as it ensures there's no lack of an heir. It was also common before reliable birth control as people often married young and were expected to have a lot of kids (partly because of high child mortality rates). Likely to contribute to a Tangled Family Tree or get older siblings asked Is That Cute Kid Yours?. Contrast Absurdly Youthful Mother, where two different generations are a lot closer to each other than is expected, and Family Relationship Switcheroo, where someone pretends their child is a much younger sibling.
To qualify for this trope, there must be at least a decade between the youngest and oldest sibling.
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- Real Life
- Ant-Man: Hank Pym's long-lost daughter Nadia (with his late first wife) is a teenager, while his son William Grant Nelson (with Tigra) is a toddler. Although technically William is the child of a Skrull who had assumed Hank's form, down to the DNA level.
- Avatar: The Last Airbender The Search: Kiyi is the maternal half-sister of Zuko and Azula, who're 14 and 12 years older than Kiyi, respectively.
- Batman's eldest adoptive child Dick is mentioned to be twenty-six in "Nightwing: 321 Days" while his biological son Damian is ten during "Batman Reborn," published two years later. Accordingly, Dick had a Promotion to Parent while Bruce was believed to be dead. Bruce's other adoptive children Jason, Tim, and Cassandra are all in between Dick and Damian in age, with Tim said to be seventeen during "Batman Reborn."
- Giant Days:
- Susan Ptolemy has six older sisters, with a sixteen-year difference between her and her oldest sister, Electra. Susan sees her sisters as six deadly enemies who've catalogued every embarrassing thing she's done throughout her life, and the only one she's shown getting along with is Bobbie, who's fourteen years older than her.
- Graham McGraw is ten years younger than his older brother Frank. Frank is fairly childish for a man in his thirties and loves pranking Graham when he visits, which brings out a more playful side of the usually straightlaced Graham.
- An unintentional example occurred with Green Arrow's sister Emiko Queen. She was originally introduced in the rebooted New 52 continuity, where Oliver Queen, a.k.a. Green Arrow (who had typically been depicted as a middle-aged man prior to the reboot) had been significantly deaged to somewhere in his 20s. As such, Ollie having a teenage sister was nothing out of the ordinary. However, DC Infinite Frontier subsequently reintroduced most of the pre-New 52 continuity, including Connor Hawke, Ollie's son (who himself is in his early 20s or late teens at the absolute youngest), which had the side effect of aging Ollie back up. As such, Oliver is once again seemingly in his 40s or very late 30s, despite having a little sister who is still in high school. This also means that Emiko is younger than Connor, despite technically being his aunt.
- Spider-Man is an orphan raised by his Uncle Ben and Aunt May, who look more like his grandparents. The usual explanation is that Ben was significantly older than his younger brother Richard, who was Peter's father.
- This comes up quite frequently with Wolverine's offspring, thanks to his Healing Factor, and he's had numerous other children over the decades. Most notably, Daken was born in the 1940s, putting him in his 70s. His sister-by-cloning, X-23 is 20. Her sister-by-cloning Gabby is physically 13 but is Younger Than They Look because she was rapid-aged to that point.
- Wonder Woman: Wonder Girl Cassie Sandsmark is several thousand years younger than her half-siblings like Hercules, Ares and Athena, whom their father Zeus fathered in antiquity. Like in Classical Mythology, it's a consequence of Zeus both being immortal and never keeping it in his pants. This is Played for Laughs when Sandsmark learns of her heritage, as she continues to idolize Wonder Woman, and Wonder Woman continues to treat Sandsmark like a younger sister or even a daughter, despite the fact Cassie is Wonder Woman's great aunt. In the New 52, Wonder Woman is changed to be Cassie's aunt due to Zeus being Diana's father, with Cassie becoming the daughter of one of his demigods instead.
- In Alice in Wonderland, Alice is a preteen, while her sister, who appears at the beginning and the end, is a young woman.
- In Barbie and the Magic of Pegasus, it's revealed that Brietta the pegasus is actually Annika's older sister, whom she didn't know existed for much of her life. Annika was born after Brietta was turned into a pegasus on her sixteenth birthday, which would make Annika at least sixteen years younger than Brietta. Funnily enough, when Annika uses the Wand of Light to turn Brietta human again, Brietta looks the same age as Annika though she should be in her thirties (it's possible magic had something to do with this). The two quickly bond as sisters despite the age gap and lack of direct interaction up to this point; Brietta also reveals that she's secretly watched over Annika all her life.
- In Barbie as Rapunzel, Prince Stefan appears to be about twenty years old, while his brother and three sisters are all about three.
- A Bug's Life: The exact ages of Princess Atta and Dot are quite difficult to discern. From what little that can be inferred, Atta might be in the ant equivalent of early to mid-twenties. Dot, on the other hand, seems to be a child approximately between the ages of 7 to 10 years old.
- In Encanto, Antonio is five years old. His two siblings and three cousins are all between ten and fifteen years older than him.
- The Incredibles: According to official sources, Violet is 14 and Dash is 10. Their little brother, Jack-Jack, is a baby.
- The Land Before Time: In VI: The Secret of Saurus Rock we learn that Cera (who, despite her Vague Age, is still a child) is an aunt to two three-horn hatchlings named Dana and Dinah, thus proving that she has at least one older sibling who is already at an age that he/she can have children. This sibling is not seen, however.
- Lilo & Stitch: In the original film, Lilo is six while her older sister Nani is nineteen, and Nani has a Promotion to Parent since their parents died. As such, she acts much more like a mother than an older sister towards Lilo. In fact, the original version of the scene in which the sisters bond after their first big fight had to be replaced at the last minute since test audiences mistook Nani for Lilo's mom instead of her big sister and people kept having zero sympathies for their plight "because it was her own fault." The revised scene makes it more clear that they are sisters.
- In The Princess and the Frog, Prince Naveen, a young adult, has a six-and-a-half-year-old brother. This is revealed as the punchline for Charlotte jokingly suggesting she could Settle for Sibling.
- During the final verse of Trace Adkins' Age-Progression Song "You're Gonna Miss This," the plumber working on the protagonist's water heater, responds to her frantic apologies that her restless children's tantrums don't faze him. As he is a father of two children himself, whom he mentions are now 36 and 23 years old respectively.
- Classical Mythology: While the age difference isn't discussed much because non-creation myths don't typically have clear timelines, the gods' Immortality and, in most cases, promiscuity, would lead to half-siblings centuries in age different at least, especially when it comes to Zeus's divine children and his innumerable demigod offspring.
- In The Bible, Abraham has two sons, Ishmael and Isaac, born fourteen years apart. Then, when both are already married adults, he marries again and has six more sons, though they're much less important to the narrative.
- Jacob's first twelve children seem to have been born during a span of about seven years (multiple wives were involved), but another seven or so years pass before Benjamin, the youngest, is born, so this would apply between him and the older ones.
- Westeros: An American Musical: There is evidence of a large age gap between Rhaegar and his younger sister Daenerys. Elia Martell and her children, who were canonically Rhaegar's wife and children, were killed seventeen years prior to the beginning of the play. Daenerys, meanwhile, has only recently gotten married when the play starts.
- Bad Machinery: Shauna Wickle is only a few years younger than her first half-brother, Darren, but she's more than ten years older than her second half-brother, Humphrey. They have the same mother but three different fathers. In "The Case of the Good Boy", Shauna complains about being forced to take Humphrey with her to a carnival because she'll get mistaken for a "pram face" (teen mom). The first time Humphrey meets Darren in "The Case of the Missing Piece", their interaction is awkward because the only thing Humphrey knows about Darren is that Darren's been in jail since before Humphrey was born.
- In Crimson Knights The Hero Judoch is roughly twenty years old at the start of the story, while his little sister Wilburg is just five.
- Extreme case in The Cyantian Chronicles: Elite wolves live for centuries, but after a civil war among the second generation the first generation refrained from having more cubs for over 400 years, only changing their minds when their age started to catch up with them. Syrys wakes up from two centuries in stasis to find he has two half-brothers with their own cubs, while Rama's half-sister Sheana is a few months younger than his bastard son Vin.
- Defied in Kill Six Billion Demons. The supplementary text reveals Solomon David has his sons in generational litters by multiple mothers and lets the older generation die off before siring a new one. He does this specifically to avoid this trope and its attendant problems of how multiple generations of mortal sons deal with having an immortal father.
- Sabrina of Sabrina Online is an adult with a job. Her younger sister Tabitha is five years old.
- Rue from Sleepless Domain is somewhere in her teens and her little brother is still a baby.
- Critical Role: Beauregard Lionett and her little brother in the second campaign. She is at least 20 years older. As soon as he was on the way, her parents had her shipped away, did everything to forget about her, and gave the new baby the place as the family's heir. As a result, Beauregard only meets her younger brother when he is already two years old and she is approximately 23.