Lopez spent much of his childhood in Greenwich Village, except for one year in Massachusetts while his father was working for Clark University. Upon their return to New York City when he was six years old, "it was a fluke" that he started piano lessons at Greenwich House Music School. The apartment they were subletting at the time happened to have a piano; his mother asked if he was interested in taking lessons, and he said yes. At age seven, his parents bought a piano for him, he saw his first Broadway show, and he wrote his first song. At age 11, he wrote his first opening number. At around age 12, he briefly moved away from the piano and tried playing the saxophone, as well as taking courses in musical composition at other music schools.