This can be a very difficult question to answer. The reason for this is that this question actually borders on a touchy topic because it involves the subject of age. Many employers today are so concerned about breeching requirements regarding the avoidance of any question that pertains to age that they steer clear of all age related questions. While you could certainly tell the interviewer that you do not feel that is an appropriate question because it involves your age, which is irrelevant to the requirements of the job, a better way to handle the question would be to present an answer that demonstrates your professionalism and experience without indicating your age.
For example, instead of saying that you were hired for your first job when you were 12 in 1968 you might instead say that you have always had an interest in being independent and that translated into first performing odd jobs around the house for your parents and grandparents and then working your way through college. Keep in mind that when you answer this type of question you are in no way obligated to indicate your age or any dates that would indicate your age. Your age is not relevant to your ability to perform the responsibilities related to the job in most cases. The only matter that should be of interest to the interviewer is your skills. Therefore, you should make sure that you keep your answer to this question focused on your skills and experience and your ability to perform the job for which you are interviewing.
An interviewer’s reasons for asking this type of question could be numerous. He or she may be making a veiled attempt at trying to discern your age and are hoping that this type of question will cause you to say how old you are. They may also be trying to find out whether you have a sufficient amount of professional experience, drive and motivation to handle the job in question. Regardless of their own motivation for answering this question, you should make sure that your answer deflects attention from your age and keeps the attention focused squarely on your skills and experience and what you can do to benefit the company. This is the best way to show that you are the right person for the open position regardless of age.