expression, adverb
unbecoming to one's age; inappropriately for one's years
Used to describe behavior, actions, or attitudes that are not suitable for a person's age, often implying childishness or immaturity. Typically modifies verbs or adjectives.
彼は年がいもなく、ゲームに夢中になっている。
He is absorbed in video games, which is unbecoming to his age.
年がいもなく派手な服を着てしまった。
I ended up wearing flashy clothes that are inappropriate for my age.