Castilla joined the Houston Dynamo pre-academy teams when he was 7.[3] In 2016, at the age of 11, he moved to the Dynamo Academy.[3] He spent some time training in Spain and with the Columbus Crew Academy before returning to the Dynamo in 2019.[4]
Professional
Houston Dynamo
On 14 June 2020, Castilla signed a Homegrown contract with the Houston Dynamo. The contract went into effect on 1 January 2021. At 15 years old, Castilla became the youngest homegrown signing in club history.[5] He spent the rest of 2020 with Houston's USL Championship affiliate, RGVFC.[6] He made his professional debut on 31 October 2021, coming on as late substitute for Memo Rodríguez in a 1–0 home defeat to the Colorado Rapids.[7] Castilla ended the 2021 season with 2 appearances.[7]
During the 2022 season, Castilla primarily played with Houston Dynamo 2 in MLS Next Pro, where he had 1 goal and 4 assists in 17 appearances.[8] His one first team appearance of the season was a substitute appearance in the Open Cup.[2]