I keep seeing people say the same thing over and over but i fail to understand what they mean. What is it that you can do in high school that you'll never be able to do again?
When you are in high school and university you can afford to spend your time on the frivolous stuff. How often since you've been a professional have you been able to take 4 months off at a time every year with another month of vacation peppered throughout the year? Of your time in high school how important, really, was the knowledge you've gained compared to the knowledge you've gained since high school? Since high school have you had an opportunity where you could not only make life-long friends, but also take social risks that wouldn't drastically affect your life for more than 4 years? Since high school have you ever been capable of having your criminal record no longer exist?
I would also add that biologically you will more than likely heal slower and probably have much more permanent damage to your body after university/as time goes on. This becomes non-trivial if you are an active person; especially if you do full contact sports.
Even by the end of university I felt like a crotchety old man after rugby games compared to highschool where I went to the emergency room a couple times and left feeling 100%
Here's another as well. In highschool and college you have the unique situation of everyone having generally the same schedule. I remember going on group vacations with 30 friends that were amazing that would be completely impossible with my schedule now. My friends and I have a hard enough time getting everyone to show up to play board games for 2 hours.
edit: You can also get lifetime scuba certification for like $50 at most schools AND GET COLLEGE CREDIT. That's like a $350 investment after you leave college (this one is half a joke, but being a student can net you tons of discounts on things you'll never be able to afford otherwise).