#1 Lio Rush (24 years old)
Even though Rezar and Liv are also 24 years old, Lio Rush is still the youngest. Lio Rush made his first televised appearance on the October 4 episode of WWE NXT in 2017, where he was attacked by The Velveteen Dream (his former tag team partner Patrick Clark). Rush was defeated by Dream in a match a few weeks later on NXT.
Rush then moved to the cruiserweight division and after weeks of vignettes, he made his in-ring and televised debut as a heel on 205 Live in June this year. He later started a feud with Akira Tozawa and picked up a win over the former Cruiserweight Champion.
He is currently the mouthpiece of the current Intercontinental Champion Bobby Lashley. He competes on 205 Live and manages Lashley on Raw. Rush could capture the WWE Cruiserweight Championship in the future as he is one of the best competitors in the division.
At the age of just 24 years old, Rush is currently the youngest superstar on the main roster in WWE.