Stanley was born in Los Angeles, California on Aug. 18, 1999. He is the son of Jerome Stanley and Tonya Sedwick. His mother competed on the track and field team at UCLA. Stanley was a four-star recruit out of high-school who was ranked as the No. 6 shooting guard in the ESPN Top 100. During his senior year at Sierra Canyon, he led the team to the California Open Division Championship, posting 20 points and even boards in the title game. He also named the 2019 Daily News Player of the Year and CIF Open Division Player of the Year on the back of 17.7 points, 6.9 rebounds and 2.9 assists. Stanley chose to go to Duke for college over Oregon and UCLA. At Duke, he was named to the ACC All-Freshman team on the back of 12.6 points and 4.9 rebounds. After that, he declared for the NBA Draft.