Cách sử dụng
The expression "if he's, she's, etc. a day" is used to refer to someone's age. It means if you guess someone's age to be a certain number, and then add one day to it, it will still be accurate. For example, if you guess that a person is 40 years old and say "if he's 40 a day," it means that the person looks like they are around 40 years old or slightly older. This expression is often used in informal conversations or when describing someone's appearance or behavior.