*Club domestic league appearances and goals, correct as of 22 November 2024 ‡ National team caps and goals, correct as of 14:19, 22 November 2024 (UTC)
A native of Düsseldorf, Castrop began his career in the youth academy of Fortuna Düsseldorf. In 2015, he transferred to the academy of Düsseldorf's rival, 1.FC Köln, where he played for the club's U15 and U17 teams. In August 2020, Castrop was promoted to the club's first team by manager Markus Gisdol. He also signed a long-term professional contract until June 2023.[2]
In January 2022, it was announced that Castrop would join 1. FC Nürnberg on a loan deal.[3] In June 2023, the club activated a €450,000 option to sign Castrop on a permanent basis.[4]