|High School:||New England Revolution Academy|
BEFORE UNH: Played with the New England Revolution Development Academy. In 2010-11, he made 12 starts in 23 appearances at the back position and helped the squad post five shutouts. In the 2011-12 season, Szostkiewicz started 26 of the 29 games he appeared in and tallied the first goal of his Revolution career. The goal came against NJSA and was also the game winner. In the same year, Szostkiewicz competed in the U.S. Soccer Development Academy Winter Showcase, making three appearances with one start. While at Longmeadow High School, the back started all games played during his time with the program. He helped lead LHS to the playoffs in 2010-11 and in 2011-2012. He was named to the First Team All-League squad as a sophomore and junior and was a First Team All-Scholastic Western Mass. selection as a junior.