From 2017 article:
BYU says avgerage age is 21.4 and LSU is 19.8
"This leads to the age disparity between the Cougars and everyone else in college football — a topic that sometimes irks BYU fans. The issue is significant enough that BYU, in its weekly game notes, releases the team’s average age — 21.4 years old — just so folks won’t think players are all 25 and up. Thirty-two BYU players are married, the university said."
"LSU’s average age, by the way, is 19.8 years old."