Wow, super impressive. Adding to the debate:  http://well.blogs.nytimes.com/2011/02/23/phys-ed-should-children-run-marathons/?_r=0

"For that study, Dr. William Roberts...medical director for the annual Twin Cities Marathon, and his colleague pulled data about every young finisher of the Twin Cities Marathon from 1982 through 2007.  ...More important, only 4 of the 310 young people throughout the entire 26 years visited the race’s medical tent, and none required interventions beyond a brief rest. The young runners’ “medical encounter rate,” the study concluded, “was half that of the adults”...

"Dr. Roberts says he hopes soon to contact past Twin Cities Marathon youth finishers to ask about the state of their knees and other vulnerable body parts today. He expects to find them all in enviable health, he said, but that’s a guess. “We need more science” about youth running, he said." 

1 more: http://www.runnersworld.com/running-debates/should-runners-under-age-18-be-allowed-in-marathons