What is the best age to start running distances longer than 15k / halfmarathon?

Question

I have a friend that is 16 and wants to do a half marathon this year. From what i know its not recommended to run great distances as a half marathon under the age of 18.

Are there any scientifical studies about age and long distance running?

Answer 1

According to an article in LiveStrong:

Distance

According to Running Times, the maximum recommended distance for young runners varies by age. Kids younger than age 5 can participate in designated kiddie events but should focus primarily on running as part of natural play. By age 5, kids are ready for light training leading up to a mile-long run. Preteens and early teens can manage 5K runs, and some early teens are ready for a 10K. Older teens are generally ready to compete on an adult level.

and

Cautions

Rapidly growing bones and muscles are increased risks for injuries such as shin splints. Undiagnosed medical conditions such as asthma or heart defects can affect a child's ability to participate in high-impact sports. Schedule your child for a full sports physical before beginning serious training. Follow the doctor's recommendations for training schedules, rest breaks and cross training in other sports. Have any injuries or persistent pain thoroughly checked. Make sure your child drinks plenty of water or sports drinks, warms up thoroughly before each workout, and cools down appropriately at the end of each session.

Runner's World also discussed running and age:

Framing marathon performance as an age issue is wrong, says Terrence Mahon, coach to Olympic marathoners Deena Kastor, Ryan Hall, and Mahon's wife, Jen Rhines. What's key, says Mahon, isn't chronological age but athletic age—a runner's history of aerobic training—and that goes for elites and nonelites alike.

In the past, coaches worried that turning to the marathon too soon would unduly shorten a runner's career. [Coach Brad] Hudson ran his first marathon at age 12. "I think it hurt my career to go to the marathon so young," says Hudson, who set his PR (2:13) at 23. Today, he doesn't advise kids to begin racing marathons as young as he did, but he says that high school and collegiate runners can handle high volumes of training if they increase their mileage gradually and take steps to avoid burnout.

What successful young marathoners like Wanjiru have in common with older ones like Tomescu–Dita is a solid mileage base. "There are athletes out there running marathons at 21, but if you look at most of them, you'll see they've had a high training volume for a good many years before they've run the event," Mahon says. "Ryan Hall and Dathan Ritzenhein were running 90 miles per week in high school, so for them to make the transition to 100—mile weeks wasn't so hard."

Obviously, young runners outside the elite ranks don't need to attain that kind of mileage. But the same principle applies—to prepare for the marathon, first build a strong endurance base, then adopt a graduated training program that builds to the marathon distance, says Jack Daniels, an exercise physiologist and head distance coach at the Center for High Altitude Training at Northern Arizona University in Flagstaff.

In the end, age is probably not the biggest factor - it's the amount of distance training that the athlete's body is conditioned for.

Answer 2

Are there any scientifical studies about age and long distance running?

See here.

In short, ages of winners in strength and speed events have historically peaked earlier than endurance events. The mean age of Olympic gold medal male winners from 1896-1980 in long distance events are relatively higher than shorter distance events.