It depends on if the interviewee is bothered by answering it or not. If you don't want to answer, you can try pushing back gently and see if they get the hint.

It depends on if the interviewee is bothered by answering it or not. If you don't want to answer, you can try pushing back gently and see if they get the hint. Maybe something like "I would prefer not to answer personal questions but I'm happy to answer any questions about my work experience and professional history" It places you in an awkward position of course. But it can't really harm your chances at that point. Your interviewer will either realize they are offside with the question and drop it and it won't really affect their perception of you, or they will insist you answer a question they shouldn't be asking and you probably shouldn't work for them anyways