John Mariani and my new M-W 11th have 1913 for "busboy."
1 January 1911, WASHINGTON POST, pg. 10, col. 5:
WAITER or busboy. 1121 4th st. nw.
(One of several classified ads--ed.)
20 August 1911, INDIANAPOLIS STAR (Indiana), pg. 21, col. 2:
WANTED--Situation: Busboy, porter or dishwasher; house man in private
family.