Ketcham was born in Englewood, New Jersey,[a] and lived in Brooklyn, New York, and North Hatley, Quebec, during his youth.

[1] After attending the Hotchkiss School, Ketcham enrolled at Yale, where he was a member of Skull and Bones and the Psi Upsilon fraternity.

[2] In a departure from past tradition at Yale, Ketcham subsequently appointed Howard Jones as the school's first salaried football coach.

[3][4] Ketcham later recalled: "I played every varsity game for three years and was taken out only once for a slight injury … I am generally credited with having developed the term 'roving center'.

[5] He saw action as a member of the 103rd Field Artillery Regiment in the Battle of Saint-Mihiel and the Meuse–Argonne offensive, being slightly wounded in the latter.