(half)Brother is 4 years older, he ran 4:28 and 9:55(school record), off of maybe 20 miles/week, ran only in season. He was 3rd at state in cross country. Far more talented, didn't like running but was good at it.
I ran 4:45/10:00, off of 40-60 miles/week year around. I never finished a seaon without getting seriously sick or injured. I was untalented (worst guy on my team the whole first season), but worked my ass off, which led to overtraining.
45 years later, I am still running 40-60 miles/week, happy to be pain-free and very healthy. He went on to become a Cat 1 bike racer for 30 years until a serious crash last year. I became a pro rock climber which I am also still doing, and I am coaching one of his former bike teammates, who is a very talented masters runner.