under age   (TTS發音)

too young； not old enough； below legal age未成年的；未到法定的年齡

    He could not join the army because he was under age. 他不能參軍，因為他不夠年齡。

    The son cannot have the control of his property，for he is under age. 兒子因為尚未成年，所以不能佔有他的財產。