The Opportunity Cost would have been incurred while they were in college, not 30+ years after. There are too many variables in play when projecting that far out

The Opportunity Cost would have been incurred while they were in college, not 30+ years after. There are too many variables in play when projecting that far out in the future, but you can make good estimates as to what would have happened in the past as an alternative to the 4 years spent in college.