I like how this whole thread is all about if a certain number of miles will cause burnout, yet not a single person is paying attention to speed work. Sure, 80+ miles per week isn't ideal for most high schoolers. But is 30 miles per week with hard speedwork really any better?
I'm not a very fast runner (barely under 5:00 and 18:00 off of 50-70mpw), though my seasons have been hampered by poor peaking and probably a lack of talent. When I run 50-60mpw consistently, I eventually reach a point where running becomes smooth and effortless (6 Mile Tempos in 6:20-30 pace, mileage 7:30-8:00). That felt nothing like burnout to me. I would go so far as to say that it's the easiest running I've ever done in my life.
You know what did feel like burnout though? 30 miles with 2-4 days of heavy anaerobic speedwork per week. I have never significantly progressed in any track or cross country season that I've ran. Running became so hard at the end of every cross country season that I was on the ground after every race, running maybe a 21 minute 5K. I had one season that I didn't significantly train before, having nothing to prepare my ligaments for the season ahead. There were several days where my ankle hurt so bad that I could barely walk. At any given time, 25% of the varsity team was either getting an MRI or aqua jogging, yet the coach was still giving out cautionary tales of 'too much mileage' and emphasizing the importance of 'grit' and 'mental fortitude' before every race. The school's physical therapist got so overwhelmed with the prevalence of running injuries that he asked the coach if there was something wrong with the team. One day later, the coach told us the importance of 'toughing it out' and only coming in if you really couldn't run. The PT was still flooded by runners and then eventually quit. The next PT that came in asked the same question. "What is up with the distance program here???" The first PT wasn't the only one who quit; half of the senior class ended up quitting before the end of high school.