Ryan Castellanos attended Cushman since he was three years old. He attended Archbishop McCarthy High School in Fort Lauderdale. In 2011, Archbishop McCarthy finished 29-3 and won the Florida Class 4A state championship. Archbishop McCarthy was recognized as the 2011 high school national champions by Baseball America, Perfect Game, USA Today and the National High School Coaches Association. Ryan was named Honorable Mention All-Broward County by the South Florida Sun Sentinel in 2011. His senior year, he helped Archbishop McCarthy to an unprecedented third-straight Florida state title when it won the 2012 Class 6A championship. He was selected in the 34th round of the 2012 MLB First-Year Player Draft by the Chicago White Sox. Instead of turning pro, he accepted a baseball scholarship to attend the University of Illinois. In two years there, he went 7-5 with a 5.29 ERA. After his sophomore campaign, Ryan transferred to Nova Southeastern University.