Most healthy young men or women from sixteen to forty years of age can be taught to fly an ordinary airplane. A great majority of these may become very good pilots for transport- or passenger-carrying machines in time of peace, but the requirements for a military aviator call for more concentrated physical and mental ability in the individual than has ever been necessary in any calling heretofore. — Brigadier General William 'Billy' Mitchell Quote, 'Skyways,' 1930