大人おとなじみる

ichidan verb, intransitive verb

to grow up; to become adult; to start acting like an adult

Describes a child or young person maturing in appearance or behavior, often with a nuance of seeming older than their age.

• 最さい近きん、弟おとうとが大人おとなじみてきた。

  Lately, my younger brother has started acting more grown-up.

• その服ふくを着きると大人おとなじみて見みえる。

  You look more adult-like in those clothes.