10,000 hours x 8 miles and hour = 80,000 miles … with highs and lows of training cyles – say 6,000 miles per year = 13-14 years to master the sport. If 5,000 miles per year = 15 years. Most kids start out much lower , so say if you started @ 10 years old, so you have only averaged 3,000 miles per year = 26 years.
10,000 hours for elites would = 90,000-100,000 miles
It just seems a bit high as your age increases, you lose a bit of performance and I think most elite runners are peaking well before 10,000 hours. Although I suppose if you add in weight lifting and drills etc it is a little more reasonable, but still a bit high I think.