I know this is high school you are talking about, but I started a topic on the kids side concerning this issue, but with Junior High Kids.
My son wrestled in the Middle School National Duals in Norfolk, VA two weeks ago. Mine you, my son is a very big 8th grader, 6'2" and weighs 220. We don't come across too many kids bigger than him that is his own age. The max grade for this tourney was 8th. He was one of the smaller heavyweights there! He had one kid that was 6'4" and weighed 260! I asked what they put in the water in those North Eastern States and one of the parents commented that kid was 15. I asked how that was possible and she said he "red shirted" that year. I could not believe it! Out of 10 matches he had those 3 days, 5 of the kids were 15. I guess I am just naive to think this didn't happen that young. I know I would never let my child stay a year back in school for that reason!!