A native of Bryan, Texas, Kolby Kubichek made the varsity team and lettered in all four years of his time at Bryan High School. In addition to pitching, he played shortstop and right field, impressing as a position player but really standing out as a pitcher. He earned a scholarship to the University of Texas and joined the Longhorns in 2019 after graduating from high school.
In his freshman year, the right-hander appeared in 14 games, starting two, and posted a 6.50 ERA in 18.0 innings, allowing 21 hits, walking 12, and striking out 15. That summer, he played for the Chatham Anglers in the Cape Cod League and was an All-Star, posting a 0.