Complex sentence: At the age of 16, he began working as an unpaid apprentice at the comics studios of Ricardo and Enrique Villagran in Buenos Aires, where his father had requested that they take him on.
Split into simpler sentences: At the age of 16, he began working as an unpaid apprentice at the comics studios of Ricardo and Enrique Villagran in Buenos Aires. His father had requested that they take him on.