[fivefifty]

Experience/training does seem to matter more as distance increases, distance runners tend to peak older than you'd think.

Also for sprinting, height matters somewhat, in particular the longer your legs the better you will be to a certain point. Being short and light tends to be better for quick off the mark acceleration, but after that it's more about having long legs and fast twitch muscle fibres to keep the acceleration and speed going for longer. For distance running having more muscle mass is somewhat of a disadvantage as it means you will likely develop more lactic acid and will probably gas out sooner, it's preferably to be lightweight develop a strong lung capacity/VO2 max so you can run fast for longer.

If the boys were taller and relatively muscular, they would naturally have an advantage at sprinting, but over distance wouldn't have as much of a natural advantage. Things like running technique, VO2 max, lactate threshold even just the mental aspects of distance running tend to take longer to develop.