Here's a breakdown:
* Origin: The idiom is thought to have originated from the fact that as horses age, their teeth become longer. This is because the enamel wears down, exposing the softer dentin underneath, making the teeth appear longer.
* Meaning: The idiom is used figuratively to describe something or someone that is old or past their prime. It's often used in a humorous or lighthearted way.
* Examples:
* "That car is long in the tooth. It's probably time for a new one."
* "He's a bit long in the tooth to be chasing after young women."
Let me know if you'd like to know more about other idioms!