I disagree with the responses you have received to date. Why? Because I was/am in exactly the same situation you found yourself--interviewing with someone who would be your superior, who is younger than you, and does not have your depth of knowledge or experience.

However, I did succeed in getting the job. I work for a woman in her 20s, I am old enough to be her mother, and I have 20 more years of experience in the field. But I was hired to be her assistant, not to be her. You need to recognize that right upfront and interview accordingly. First thing is you have to be very tactful in interviewing with a potential supervisor in this situation. Once you sensed that you "knew" more than this individual and that there could be resentment on his part, you needed to turn the interview around--ask questions of him, find those areas in which your supervisor excels that you don't, and there must be some, otherwise he would likely not be in a supervisory position. Each person in a case like this brings strengths, and each needs to acknowledge that. You need to make the interviewer feel comfortable with you. I could tell that my future boss was a bit unsure/nervous when she was interviewing me, and I really tried to put her at ease. As it turns out, we discovered in the course of the interview that I had a lot of experience & knowledge in an area she admittedly didn't, and didn't particularly care for. And I enjoyed that area. So we have sort of naturally "split up" the workload along those lines. As it also turns out, this firm DID need someone with my background--the perception initially may have been that I was overqualified, but only because I was used to making more money than they could offer--not because they didn't need my skill level. There is no way in hell a lesser-experienced person could have walked into my job and "hit the ground running." Fortunately my boss recognizes that and lets me know! And, fortunately for me, she does those things I am no longer interested in doing--doing the tradeshow circuit, pressing the flesh with business partners, giving presentations, etc. She's good & fresh at it, I've been there, done that, am tired of it.

So it has worked out well in this case. It can be a dicey situation, but I believe there are probably things you could have done in that interview that you probably didn't. Don't "ramp down" your experience in cases like this, but be tactful, show interest in what the younger person does and what he/she brings of value to the table, and don't give the impression that you know it all. You may not have intended to do so, but to a younger, more insecure person, you may have come across this way.

It is NOT an impossible situation, and this instance certainly does not mean that you were way overqualified for the job. Actually, with a far more inexperienced supervisor, they probably DID need your level of expertise. But it sounds like you did not make your potential supervisor feel comfortable with you, and that you must do if you are to succeed in this situation.

Good luck!