Why limit the number of years at all?
If a player wants to play college football for 15 years or more, why is that a problem.
If the pros come calling, then leave.
If you lose your starting role, then leave.
If you graduate, then leave.
Otherwise, why is staying a problem?
Before anyone says, “because that is not what we have being doing”, consider how many other things have changed over the years… portal, NIL etc.