Education
Kitur attended and ran for Albemarle High School. His coaches at Albemarle were "Buz" Male and Lance Weisend. In 2010 Kostelac was named Burger King Male Student Athlete of the Year.
In the years Kostelac attended Albemarle, the high school fielded a historic 4 × 800 men"s relay team including Kostelac, Zach Vrhovac, Luke Noble, and Garrett Bradley.
The four-man squad would set an indoor world junior record in 2009 at the Boston Indoor Championships. They were also successful on a national level in the outdoor season, as the Albemarle 4x800 relay team would win a tightly-contested 2009 Penn Relays high school 4x800 relay race.
Kostelac, Albemarle"s anchor runner, got the baton behind Morris Hills High School"s Liam Tansey, whose team was on the verge of winning the race before Kostelac (a junior during this season) took the lead in the last 175 meters and held it to win the race. By the time he graduated from Albemarle, he was a high school record-holder in the 800 meters for the state of Virginia.
Kostelac graduated in 2010 with a 3.9 Grade Point Average.