Oromo farmer would be fast
The Oromos are pastoralists, chasing cows and goats around. That's what is thought to have provided selection pressure resulting in Oromos and Kalenjins becoming fast runners. Sub-15 first time out.
"The reigning theory in the West is that runners from east Africa have some evolutionary advantage over runners from other backgrounds. Because so many of the elite runners come from the Oromo ethnic group in Ethiopia and the Kalenjin tribes in Kenya, it is assumed these groups must have adaptations or environments that make them faster. Perhaps it was their pastoralist fathers and grandfathers who spent generations running after cattle. "