A two-sport student-athlete during his time at Southeastern Massachusetts University, Ahern helped establish the legacy of ice hockey at the University. Originally recruited to play soccer, he read in the school newspaper that the then-club hockey team at SMU was going to transition to a varsity sport. Ahern went home to grab his hockey equipment and try out for the team.
 
Ahern played two seasons of soccer at SMU under head coach John Barrett, helping the team to a 25-5-6 overall record in that time. That team made two postseason appearances, including a win over Rhode Island College in overtime of the NAIA District 32 Playoffs. SMU finished second overall in the tournament that season.
 
Ahern tried out for head coach Joe Prenda's team in 1974, and made the team, having never played high school hockey outside of several traveling teams. His lack of high school hockey didn't stop him from leading the squad in scoring for the three years he played at SMU. In 50 games played, he notched 64 goals with 37 assists for 101 points. His senior season saw him named captain of the squad as well. Ahern averaged 2.00 points per game in his career, a mark that was not eclipsed until nearly a decade later.