ichidan verb, intransitive verb
look grown-up; act mature; be adult-like
Describes a child or young person who seems more mature than their age in appearance, speech, or behavior. Often used in the past tense (大人びた) or te-form (大人びて).
彼女は年のわりに大人びて見える。
She looks mature for her age.
その子は大人びた口調で話した。
The child spoke in a grown-up tone.