Think before you leap
Don't rush into something and then tie yourself in knots. It is okay to take a few seconds to think and formulate your answer, especially to important qualitative questions. This shows you are thinking and not just spurting out answers at random.
However, when asked for you birth date, answer instantly!
Remember, even for complicated answers where you need a few moments to think, don't be silent for too long or the interviewers will wonder whether you know the answer at all!