Sergeant Major Castillo enlisted in the Marine Corps in February 2000. After completing recruit training aboard Marine Corps Recruit Depot (MCRD), San Diego, CA, Private First Class Castillo attended Marine Combat Training aboard Camp Pendleton, CA. He was transferred to his Military Occupational Specialty School (MOS) aboard Marine Detachment, Navy Supply Corps School, Athens, GA. He was meritoriously promoted to Lance Corporal in December 2000, and received the MOS 6694 Aviation Information Specialist.
Lance Corporal Castillo reported to Aviation Information Systems Department, Marine Aviation Logistics Squadron 31, Beaufort, SC in August 2001. Lance Corporal Castillo was meritoriously promoted to the rank of Corporal in June 2002. In April 2003, Corporal Castillo was selected as the Noncommissioned Officer of the Quarter for 2nd Marine Aircraft Wing and meritoriously promoted to Sergeant in May 2003.
In January 2005, Sergeant Castillo reported to Drill Instructor School, Class 2-05, MCRD, San Diego, CA. Upon graduation, he was assigned to Hotel Company, 2nd Recruit Training Battalion serving as a Drill Instructor, Experience Drill Instructor, and Senior Drill Instructor. In December 2006, Sergeant Castillo was reassigned to Receiving Barracks Company where he served as Drill Instructor and Chief Drill Instructor, Recruit Separations Platoon. In March 2007, Sergeant Castillo was promoted to Staff Sergeant.
In May 2008, Staff Sergeant Castillo reported to Marine Aviation Logistics Squadron 11, Aviation Logistics Information Management and Support (ALIMS) Department. Staff Sergeant Castillo deployed in support of Operation Iraqi Freedom (OIF) 08.2 and Operation Enduring Freedom (OEF) 10.1 with Marine Aviation Logistics Squadron 16 (Forward). In February 2011, Staff Sergeant Castillo was promoted to the rank of Gunnery Sergeant.
In April 2012, Gunnery Sergeant Castillo was selected for Assistant Marine Officer Instructor (AMOI) Duty at the University of Idaho and Washington State University. While serving as AMOI, he completed four increments at Officer Candidates School as a Sergeant Instructor and Platoon Sergeant. In April 2015, he was frocked to First Sergeant, and reported to Site Support, Lubbock, TX. He served as Inspector-Instructor, First Sergeant for Motor Transport Company, Combat Logistics Battalion 453 from May 2015 to May 2018.
In May 2018, First Sergeant Castillo reported to 2d Battalion, 7th Marine Regiment, 1st Marine Division and assumed the duties as Company F, First Sergeant. In November 2019, he was promoted to Sergeant Major.
In December 2019, Sergeant Major Castillo reported to Site Support, 5th Battalion, 14th Marine Regiment to serve as Inspector-Instructor, Sergeant Major. In February 2022, he assumed his current duties as RS Albuquerque, Sergeant Major.
Sergeant Major Castillo's personal decorations include the Meritorious Service Medal, Navy Commendation Medal with 3 gold stars in lieu of fourth award, and the Navy Achievement Medal with 3 gold stars in lieu of fourth award.