Basic Trope: A character's younger sibling acts mature for their age, often in stark contrast to their older sibling.
- Straight: 8-year-old Bob is a Child Prodigy who gets straight A's in school and works on weekends to support his family's income, while his older sister, Alice, is Book Dumb and forgets to do her homework and chores.
- Exaggerated:
- Bob graduates college and leaves home at the age of eight, while Alice is still in diapers at the age of eighteen.
- Bob is a gentle Nice Guy, while his older sister, Alice, is a Psychopathic Womanchild who was imprisoned for murdering their parents for irritating her and trying to murder Bob for having a different favorite color than her.
- Downplayed: Bob occasionally acts as the voice of reason to Alice, but he also has a tendency to act snarky towards her.
- Justified:
- Bob is Wise Beyond His Years.
- Alice has a mental problem which causes her to act like a Childish Older Sibling.
- Their parents learned from their mistakes in raising Alice and were more attentive to the problems Bob had, but they had to admit that it was a little too late for Alice herself.
- Bob is Alice's long lost brother; he had to mature quickly to survive on the streets.
- Inverted:
- Subverted: Bob's maturity turns out to be a façade to hide his insecurities about being the youngest in the family. Ditto for Alice's immaturity, only she acted childishly to make her little brother feel superior to her.
- Double Subverted: Bob and Alice both have an older brother which causes their roles to reset, both of them serving as Annoying Younger Siblings to him.
- Parodied:
- Bob kills his and Alice's parents so he doesn't have anyone holding authority over him, thus proving to Alice that he's too mature for his age.
- Bob, an 8 year old, acts a lot like an adult; He drinks hot chocolate as a substitute for coffee (though he may get a mocha every now and then), drinks cola and sodas as a substitute for beer, and even wears a suit and tie to school. He often acts as if Alice is incapable of taking care of herself (though he's often proven right time and time again) even though Alice is in her friggin' 20s.
- Zig Zagged: Bob goes from an Annoying Younger Sibling to the man of the house when their parents are gone, while Alice fluctuates between being the voice of reason to a full-on Childish Older Sibling.
- Averted: Bob and Alice get along fine and have no power dynamic.
- Enforced: "Bob is a Child Prodigy. He has to have some power over his older siblings."
- Lampshaded: "At least I wasn't dropped as a baby."
- Implied: Alice claims that her younger brother acts mature for his age, but said brother is never seen in the work.
- Invoked: Bob only acts mature because he wants to stand out as the youngest in his family.
- Exploited: ???
- Defied: Bob acts like a typical kid brother, because he knows it's too unrealistic to have power over someone with more experience than you.
- Discussed: "Bob, you're acting too mature for your age."
- Conversed: "I wish your brother could be more like mine."
- Deconstructed: ???
- Played For Laughs: Bob is shoehorned in the work as as a mature younger sibling because the writers know it will further help establish the protagonist's Butt-Monkey status.
- Played For Drama: Bob was deprived of his childhood by being forced to become jaded at a very young age, while Alice suffered a head injury as a toddler which resulted in her mental deficiency.
Back to Mature Younger Sibling.
