At age 26, Castrillo attended the Santa Isabel de Hungria School of Fine Art in Seville where, over a two-year period, he acquired a great deal of experience with brushwork techniques and figure drawing. He was also enriched by his many contacts with the other students and master painters at the school. Castrillo’s friendship with the celebrated Sevillian painter Joaquín Saenz played a significant role in his education as a painter, and increased his knowledge of the works of such Masters as Leonardo da Vinci, Rembrandt, Renoir, and Velasquez above all.

In 1989 Castrillo married Trinidad Fernandez, a fellow painter, with whom he has enjoyed many collective exhibitions. Castrillo has also had numerous solo art exhibitions showcasing his landscapes, which feature many places and landmarks from his beloved Seville. Currently, Castrillo teaches painting classes to a very small, elite group of about twenty students, and does research in the field of New Age painting - the form of expression he uses at present in his paintings.