I was hoping you could tell me what "training" you would change if you could go back in time.
My training was always great because I had great coaches. My youth and high school coaches always kept it fun and challenging. In college, it was intense and moderate mileage. I could have better supported the training by sleeping and eating better. Our bodies can handle a great deal of work if we are rested and well hydrated/nourished. Big miles and intense workouts are doable if you are having intense rest days too. So, going back, I guess I'd make sure my recovery days were a bit more restful.