Normally you expect families to adopt children, but in these cases the adoptee is a full grown adult.
Usually Played for Laughs
because of how absurd it seems.
Anime and Manga
- In Samurai Sentai Shinkenger, Kaoru adopts Takeru before stepping down as head of the Shiba Clan, making him the real lord instead of a decoy.
- Kami no Shizuku: Wine critic Tomine is adopted by Shizuku's father Yutaka shortly before his death, with the goal of inheriting Yutaka's vast and valuable wine collection. The plot becomes a Game Between Heirs to see who inherits the collection.
- One of the Superman Bizarro comics had a child adopt an adult.
- In Stuart Little, Stuart was 18 in mouse years when he was adopted by the Littles. Not that extreme an example, but still technically an adult.
- In Little Shop of Horrors, Mushnik adopts Seymour for his money. Seymour is at least in his late teens.
- Juda Ben Hur is adopted and made a Roman citizen by the tribun whose life he saved.
- On an episode of The Munsters, Lily adopted an amnesiac Herman.
- Discussed on Boy Meets World. After Shaun's father dies, his best friend Cory's family offers to adopt him. He is touched but ultimately declines.
- Discussed in Calvin and Hobbes, when Calvin's father thinks, in a moment of exasperation, "We should've adopted a twenty-five year old with his own apartment."
- In Something Positive, Davan's parents adopt his acquaintance Monette after she moves in with them following a bad breakup.
- On The Cleveland Show in the episode "Hustle 'N' Bros" Cleveland's father adopts Donna's ex-husband Robert.
- In the Dan Vs. episode "The Ski Trip" an overly cheerful family Chris meets bond with him and plan to adopt him.
Chris: I'm kind of an adult.
Mrs. Pleasant: Don't worry about the rules. We have a friend in social services.
Chris: And I have a wife.
Mr. Pleasant: We'll adopt her, too!
Chris: But then I'd be married to my sister...
- During some periods of the Roman Empire, it was customary for a patriarch of the family to formally adopt an unrelated-by-blood but capable (adult) successor. One famous example would be the first Roman Emperor Augustus, who was adopted by Gaius Julius Caesar at the age of 19. Likewise, all of the Five Good Emperors were adopted by their predecessors into the Antonine family at adult ages.