[2][3] He was the youngest of eight children of the noted Peruvian painter Teófilo Castillo Guas, and María Gregoria Gaubeka, originally from the Basque Country in Spain.
Initially, Castillo took up photography, a trade passed down from his father and practiced by his older brother, while dedicating his free time to painting.
In 1940, committed to pursuing his passion for art, he relocated to Buenos Aires to study drawing and painting at the Sociedad Argentina de Artistas Plásticos and Art History at the Faculty of Philosophy and Letters of the University of Buenos Aires.
[2] At the National University of Tucumán, he expanded his artistic horizons and began teaching, serving as director of the province's Escuela Infantil de Artes Plásticas.
He also experimented with stage design and directing for the Nuevo Teatro de Ofelia Woloshin group.