noun which may take the genitive case particle 'no', noun
age-appropriate
Describes something suitable for one's age, especially clothing, hairstyles, or behavior. Often used in the phrase 年相応の～.
彼女は年相応の落ち着いた服装をしている。
She dresses in a calm, age-appropriate manner.
年相応の振る舞いを心がけなさい。
Try to behave in a way that is appropriate for your age.
More formal and explicit synonym using 年齢 (age). 年相応 is slightly more colloquial and common in everyday speech.
Compound of 年 (とし, 'age') + 相応 (そうおう, 'suitable, appropriate'). The reading としそうおう is a straightforward combination of the two components.