Knighton, in case you're unfamiliar with him, ran 20.33 last summer at the AAU Junior Olympics. He was (and still is) 16 at the time, having just finished his sophomore year of high school in Tampa. He's 6-foot-3 and looked like a man amongst boys:
https://www.youtube.com/watch?v=G8QKrIES0Zw&feature=emb_logo
To my knowledge, this is the earliest a US male track & field athlete has ever turned pro. I know Candace Hill turned pro at 16 after her sophomore year in 2015. I can't remember anyone else turning pro before the end of their junior year.
Obviously there's a degree of risk here, but 20.33 is ridiculous for a 16-year-old. adidas has had success with Drew Hunter and Noah Lyles out of high school, which likely contributed to their decision to sign Knighton.
https://trackandfieldnews.com/teen-sprint-sensation-erriyon-knighton-goes-pro/