spring chicken

Today's idiom is especially dedicated to one of my daughters

While there is actually a bird called a spring chicken, which on the menu is often referred to as "poussin" (a young bird with more white than brown meat) we frequently use this term to refer to a young person who is full of the vitality of youth, and maybe a bit naive.

More often it is used in the negative to say that a person is no longer young, and maybe a bit slower than in the past or not up-to-date with the latest ideas.

e.g. Larry's incredible - he still goes running 30 miles a day, even though he's no spring chicken!

Another common expression is to do something "like a headless chicken" (no picture for this one!), that is to do lots of things in a hurry and without thinking too much. This is normally used with progressive tenses.

e.g.

I've been so busy this week that I've been running around like a headless chicken.

There are many more chicken expressions, but as regards the eternal dilemma of "which came first, the egg or the chicken?" I refer you to the answer suggested below!