Related, for me, was that high school just wasn't very challenging. I got As without ever really studying or feeling that I was working very hard. I took that approach into university and it worked for my freshman and most of my sophomore courses. Then things got actually tough and I realized I could not just intuit my way through exams, and I had never really learned how to study.

Every undergraduate student I met over the age of 22 was much, much better than their young counterparts within the same ability cohort.