Castillo began his career with a club named "Cardozo" and the Escuela Carlos Sarmiento Lora, before joining Fortaleza C.E.I.F. at the age of sixteen.[2][3] In March 2021, following his first full season with the Fortaleza first team, he was named by the CIES Football Observatory as one of the most promising young footballers in the world.[4] In pre-season ahead of the 2023 season, he gained national attention after performing a "scorpion kick" save, popularised by compatriot René Higuita.[5]
International career
Castillo has represented Colombia at under-15, under-17 and under-20 level.[1][4] He was called up to the under-20 squad in March 2023, but found himself culpable for two mistakes leading to goals in the 2–0 friendly loss to Wales.[6] He was called up again ahead of the 2023 FIFA U-20 World Cup, stating that the opportunity was a "dream come true".[3]