Hill was born on December 20, 1983, in Los Angeles, California, to Sharon Lyn (née Chalkin), a costume designer and fashion stylist, and Richard Feldstein, a tour accountant for Guns N' Roses. He has a younger sister, actress Beanie Feldstein (born 1993); their elder brother, Jordan Feldstein (1977–2017), was a music manager of Robin Thicke and Maroon 5 until his sudden death at age 40 from a DVT/pulmonary embolism. His parents were originally from Long Island, New York, and the family vacationed in the Catskills. He grew up in the wealthy Los Angeles neighborhood of Cheviot Hills, where he continues to live, and attended the Center for Early Education, Brentwood School, and then Crossroads School, in Santa Monica. He worked at Hot Rod Skateboard Shop on Westwood Blvd in Los Angeles. After graduating from high school in 2002, he attended The New School and the University of Colorado Boulder, but did not earn a degree. Hill is Jewish, and had a Bar Mitzvah ceremony.