So now that there is a story linked...the story misses the point. The issue is not acute injury, which is what the article discusses, but long-term injury by over training adolescents before they are ready.

Marathon training involves base training to bring up mileage to a minimum number (we can debate what that number is, but it's over 20 miles a week). Base training is followed by a 16-20 week cycle of increasing mileage and increasing the length of individual runs. Training will involve at least 3 runs over 3 hours in length. At a cadence of 180 foot strikes a minute each of those long runs produces 10,800 foot strikes an hour or somewhere from 30,000-40,000 foot strikes in a single session. And there will be 3 or 4 other sessions in a week.

Is that something developing bones should be exposed to? What are the long-term implications of exposing open growth plates, partially calcified bone, and immature connective tissues to high loads of repetitive stress?

Running has taken generally taken a conservative approach and limited mileage for younger participants. High schoolers focus on short distances, generally under 5000 m.