Justin Gatlin vowed to retire after the 2020 Olympics, but the 38-year-old USA track star tells TMZ Sports plans change, 'cause he ain't quittin' before takin' another crack at gold ... thanks to some inspiration from Tom Brady.
We talked to the LEGENDARY sprinter -- who competed in the '04, '12, and '16 Olympics and won 5 medals including a gold in the 100M in 2004 -- and asked him straight-up, are you retiring??
Nope ... "The goal will be to compete in the 2021 Summer Olympics," Gatlin tells us.