In all the world, Castiillo (Castiillo 
) is an extremely rare unknown gender first name. Much more frequently, Castiillo is the last name as well as the forename.
Ale, John, Joel, Juan, Vane, Faby, Yuly, Maria, Mariu, Marii, Marco, Monse, Melii, Mimii, Susan, Sonia, Sonii, Sofii, Alexa, Aleja, Aliin, Andii, Jose, Lula, Luis, Liiz, Ana, Pao, Gre, Eva, Mary, Sara, Saul, Alex, Alee, Alan, Angel, Abii, Barb, Beny, Kiim, Pato, Paco, Raul, Rene, Ruby, Ruth, Lili, Axel, and Camii