Agate, the eldest child of Charles James Agate (1832–1909), a wholesale linen draper, and Eulalie Julia "née" Young, was born in Pendleton, near Manchester, England. His father had a keen interest in, and connections to, music and the theatre. Gustave Garcia, nephew to the "prima donna" Maria Malibran, was Charles's lifelong friend since they were apprenticed together in the cotton warehouse. Agate's mother was educated in Paris and Heidelberg, and was an accomplished pianist. Through Agate's family connections to the active German artistic community in Manchester, he had much exposure to performance in his youth. In October 1912, Sarah Bernhardt visited the Agate home, an indication of the family's position in the local arts scene. Agate's only sister, May, later studied acting under Bernhardt in Paris.