We have had two state medalists recently, both were among the youngest kids in their classes. One of them was 17 when he graduated, he is currently wrestling at the division 2 level. Our best freshman this year was the youngest on the team.
Starting boys late has some major advantages socially, academically, as well as physically. I would argue that more parents should be starting their boys late if possible, the benefits mostly outweigh the costs.
On a similar topic I would be interested to see how well these athletes do in college when all the physical advantages have essentially been erased since everyone has matured physically.