A 2020 graduate of Montclair State University, Kirn appeared in 48 career games for the Red Hawks while serving as captain his senior season. A 2019 All-Conference first team defenseman, Tim registered 49 ground balls and 40 caused turnovers over his four seasons at Montclair.

Playing his scholastic lacrosse at Bridgewater-Raritan High School in Bridgewater, N.J., Kirn was an All-State selection and a senior captain (2016) for the Panthers.