What is the origin of the idiom "young blood" and when to use it?

The phrase likely originated from the relation of youth and vitality to describe the qualities or characteristics associated with youth, such as vigor, vitality, and freshness. It is often used to refer to young people, particularly in the context of their energy and enthusiasm. However, it is worth noting that the use of this idiom can sometimes carry connotations of ageism or discrimination against older individuals, so it is important to use it with sensitivity and consideration.