Difference between training and over doing it

What determines how hard someone should train? Results? Coaches? Parents? Level of Play? Recently I committed to Molloy College where I will be playing division 2 baseball for the next four years. Since I was in my Junior year of high school I have been training for college baseball. When I found out where I was going, a spark was ignited inside me. Since then I have made huge strides in weight gain, muscle mass, and endurance. The problem however, am I over doing it. Last week was a slow week for me due to the schedule that I had at school. I tracked the number of hours I spent at baseball, in the gym, and during endurance training, the results I received we're astonishing. I spent 40 hours outside of school working on improving myself for baseball and overall physical well-being. That means that I am spending an average person's work week, bettering myself as a player. So I began to ask myself if I was pushing it to hard, if maybe I needed a break. High school athletes going to college to play their sport are expected to exert all excess energy outside of school to their sport, but my question is, where is the line drawn and when should an athlete not only want to stop, but be forced to stop for their own well being? The peak physical shape for a male human is 28 years old and at that age it is crucial to better yourself physically because most likely, the body type that you have at around that age is the one that you'll have for the majority of your life. An 18 year old however, a SENIOR in high school, is TEN YEARS away from that peak point, most however push themselves harder and see maybe half of the results. Should we limit our children's energy exertion or should they manage it themselves? Where is the line drawn.