Eng: Immature...

嫩

Delicate, Immature, Light, Tender, Young

幼

Immature, Young

稚

Immature, Infantile, Young

幼稚

Childish, Immature, Naïve, Unsophisticated

不熟

Immature, Unfamiliar

不懂事

Immature

(Don't understand, Not understand, Makes sense, Sensible)