What is the origin of the idiom "salad days" and when to use it?

The idiom "salad days" has its origin in Shakespeare's play "Antony and Cleopatra," where it was used to describe a period of youth and inexperience. In the play, the character Cleopatra refers to her youthful and carefree days with Mark Antony as her "salad days." Over time, the term has come to mean a time of youthful innocence, inexperience, or a period of carefree and untroubled existence. It is often used to refer to a time in the past when someone was young and inexperienced, or to describe a phase of life when one was less burdened by responsibilities and worries.