Penny played in 23 games (14 starts) in two seasons at Idaho after transferring from Cerritos (Norwalk, Calif.) College. He totaled 1,748 yards and 22 touchdowns on 385 carries with the Vandals while adding 39 receptions for 346 yards and three scores. In his first season at Idaho in 2014, he rushed for 12 touchdowns, the most by a Vandals player since DeMaundray Woolridge had 18 in 2009. Prior to transferring to Idaho, he ran for 1,338 yards on 199 carries and scored a school record 20 touchdowns as a sophomore at Cerritos College. He was named first-team All-American and the Northern Conference Offensive Player of the Year.

His brother, Rashaad, was a first-team All-American running back at San Diego State and led the NCAA with 2,248 rushing yards in 2017. Rashaad was drafted by Seattle in the first round (27th overall) of the 2018 NFL Draft.