In 2008 , at the age of 21 , he began fighting professionally at a rapid pace .
Johnson 's upstart mixed martial arts ( MMA ) career was spurred through the training he received at The Springfield Fight Club .
In 2008 , at the age of 21 , Johnson began fighting professionally at a rapid pace .
Johnson 's upstart mixed martial arts ( MMA ) career was spurred through the training he received at The Springfield Fight Club .