After starring for Hinsdale Central High School, Allen was recruited to play college football for Michigan State University.

Allen was selected by the Los Angeles Rams in the fourth round (111th overall) of the 2018 NFL draft, using the pick acquired in the Robert Quinn trade.

Prior to the 2023 season, Allen sat out due to injury and was replaced by teammate Coleman Shelton for the starting center position.

[10][11] His older brother Jack is also a center who signed a free agent deal with the New Orleans Saints in 2016.

All 3 brothers were Illinois high school HWT state wrestling champions.