an old head on young shoulders

【字面理解】在年轻的肩膀上有颗年老的头

【英文解析】It’s used to describe a young person who acts in a more sensible way than you would expect for a person of their age.

【中文解析】年轻而有见识;少年老成

【典型例句】① He’s only seventeen, but he has an old head on young shoulders and remains calm under pressure. 他只有17岁，不过却少年老成，面对压力沉着冷静。

② That man would do this job very well, for he clearly has m old head on young shoulders.那人虽年轻却很有头 脑，能把工作干得很好。

【注释】源自莎士比亚的戏剧《威尼斯商人》(TheMerchant of Venice) ： I never knew so young a body with so old a head.(盖如此少年老成之士，实鄙人生平所仅见也。)