[4] Castillo qualified to the 2008 Olympic Games in Guatemala in April 2008,[4][5] and in May he won the gold medal at the Cheo Aponte Cup in Caguas, Puerto Rico.
[10] One month later, in May he won by unanimous decision to the Mexican Alvaro Enriquez to improve his record to (5-0-0) in a fight held at the Seminole Hard Rock Hotel and Casino in Hollywood, Florida, United States.
[11] In July, he knocked out the Mexican Ricardo Campillo in the second round in a Light Heavyweight category combat held in Hollywood, Florida, improving his record to 7-0.
After fighting six more times, with a record of 5-1 (the loss coming to Marcus Browne), Castillo challenged Dmitry Bivol for his WBA (Super) light-heavyweight title on October 12, 2019.
On September 25, 2021, Castillo suffered a brutal knockout loss to Callum Smith, on the undercard of Anthony Joshua’s world heavyweight title defence against Oleksandr Usyk.