Many people wondered if I was a student or a professor, but one of the things that is great about academics is that it is almost purely merit-based. It does not matter how you look, how you dress, or how you act. Once you establish that you are an expert in your subject and have good ideas, you immediately earn people's respect. Youth is to some extent viewed favorably (unlike in other professions that have a strict ladder system) since breakthrough discoveries are often made when people are young. My colleagues treated me like anyone else in the department as soon as I arrived at Berkeley, even though most of the graduate students in the department were older than me.

With the students, I tried to take advantage of the fact that I was roughly the same age as them to make it easier to approach the professor. In one of my classes, my teaching assistant (a graduate student) and I started the class with a practical joke. She began the first lecture and pretended to be the professor. I sat in the back, dressed informally like the other students. I started raising several questions once she started the lecture, eventually asking whether she was really qualified to teach the class. I then suggested that perhaps I should teach the class myself. The students were quite surprised that one of their peers would be so brash. She said, "Sure, why don't you give it a try?" I got up and began teaching. The students figured it out and enjoyed the joke. It was particularly funny because one of the students asked me while I was sitting in the back if I knew whether this professor was supposed to be hard…

How did your interest in economics originate?

I was interested in research and science, partly because I was exposed to it from my family, everyone being a PhD or MD and involved in research to some extent.

I was born in New Delhi, where my father [V K Chetty] was at ISI [the Indian Standards Institute] and my mother [Anbukili Chetty] was a pediatric pulmonologist at AIIMS [the All-India Institute of Medical Sciences]. We moved to the US when I was 9 and I grew up mainly in Milwaukee. When I was in high school, I thought I would follow in my elder sisters' footsteps and be a scientist. I worked in a microbiology lab for two years in high school and published a paper in electron microscopy staining techniques.

But after some time, I decided that I was better at thinking about conceptual problems than doing lab work. I had always been interested in doing something I felt would have a big impact on human welfare. I knew a little about economics from my father, and it struck me as a good way to combine my interest in math and more technical research areas - thinking about how to tackle hard problems such as poverty and growth to have a big impact on society.

I wasn't sure exactly what I'd pursue at Harvard, but decided to take an intermediate microeconomics course my first semester. It was taught by Andrew Metrick who is now at the Wharton School at Pennsylvania. He is a phenomenal and inspiring teacher. A few weeks into the class, I decided that I really liked the subject. I e-mailed several professors to try to get hands-on experience in research in economics. Martin Feldstein, one of the most senior economists at Harvard and former chief economic adviser to Ronald Reagan, replied to my e-mail and hired me as a research assistant when I was a 17. I quickly got involved in the projects he was working on at the time.

What fascinated me most was Feldstein's ability to go from rigorous, abstract mathematical arguments to empirical analysis of real-world data, and ultimately to a clear, concrete policy recommendation to the government.

In my sophomore year, I began to take PhD courses in economics. I found them so interesting that I completed the graduate coursework and qualifying exams the next year. Soon I was writing my PhD dissertation.

Image: Professor Martin Feldstein (L) Harvard University was the first person to recognise Chetty's talent. Photograph: Alex Wong/AFP/Getty Images