Armstrong, who is a native of Flint, Michigan, played basketball for several high schools, spending his final two year at Bella Vista Prep.
A consensus four-star recruit, he drew interest from several major NCAA Division I programs and committed to Arizona before choosing to immediately play professionally in the NBL.
[2] As a freshman at Carman-Ainsworth High School in Flint, Armstrong began playing basketball under head coach Jay Witham in the 2015–16 season.
[11] Armstrong was forced to sit out his sophomore season after being ruled ineligible by the Michigan High School Athletic Association (MHSAA).
With Bella Vista Prep and on the Amateur Athletic Union (AAU) circuit, he saw his national ranking rise again.
[20] On October 24, 2018, Armstrong committed to play for NCAA Division I basketball for Arizona, attracted by its coaching staff and environment, as well as his team fit.
[22] Sources: On June 19, 2019, Armstrong revealed his intentions to skip college basketball and instead play in the NBA G League or in another country.