He joined the club's academy in 2017 and played for their reserve team Seattle Sounders FC 2 the following year.
Castro played college soccer with the Washington Huskies and the San Diego State Aztecs from 2019 to 2022.
[2][3] He made his debut for USL club Seattle Sounders FC 2 on August 19, 2018, in a 4–1 loss to Portland Timbers 2.
Castro then transferred to the San Diego State Aztecs in 2021, where he played 17 matches and earned seven shutouts.
[2][6] Castro signed a professional contract with Seattle Sounders FC on December 13, 2022, becoming the club's 21st Homegrown Player.