Why are not you earning more money at this stage of your career?
Alternately, “Why aren't you earning more at your age?” or “Do you think you are being paid enough?”
The interviewer is not trying to insult you or indicate that you should be making more money. Instead, the reason behind this question is to find out how important is money to you, in addition to finding out what you think you are worth. If you have doubts about your skills, then you would be willing to settle for earning less.
The manner in which you answer also tell them a bit more about you as a person. If you get defensive or angry then you may have reservations about how much you are earning. If you respond in a calm and positive manner, then they may be able to see how you deal with a difficult client or perhaps a co-worker, or your team if you are being assigned one.
The trick here is to be calm and collected. Don’t feel like you have to justify why you are earning what you are earning, or that you feel you should be earning more. Instead focus on saying something along the lines of the work you are doing is your own reward, or something equally cheesy. But don’t let your answer become completely generic otherwise the interviewer will know you are not being truthful.
Instead, focus on why you are happy with what you are earning. Be confident in your answer so that it seems like that is truly how you feel. You can also highlight other things that you have earned in lieu of money, such as new skills, experience, or even the relationships you’ve made over the years with your employers and your colleagues, and especially your clients. Make it sound like you are not materialistic or money minded, and instead can find happiness and fulfillment in other things. This in turn becomes a testament to your good character.
You can also use the answer to talk about your long terms goals and how your previous job helped you with those goals. You can mention how making headway in your goals was what made the limited income worth it.
Sadly, we do live in a materialistic world. While making money is important, we often lose sight of what is important, such as the skills and relationships that make living worth it. I chose to work for a lower income rather than go for another job because I felt that this position put me closer to my goals. It offered me the chance to work on new cutting edge technology which was not even out on the market yet. That experience was worth much more to me than money. Honestly, I would have loved to do that while earning more money, but sadly for my previous position I had to pick money over skills.