Helfet attended Mark Day School for elementary and middle school and Redwood High School, where he played football, basketball, and lacrosse. As a senior, he recorded 42 receptions for 811 yards and earned first-team all-conference honors. He was lightly recruited by college football scouts, only receiving attention from FCS football programs including the University of San Diego and various Ivy League programs. However, he committed to Johns Hopkins University on a full lacrosse scholarship.
