From Rocklopedia Fakebandica
Regular Show (first aired 20 Sept 2010). Their demographic, as established in the episode, is 11- to 15-year-olds. Mordecai claims to have outgrown them, but he and Rigby still spend many hours working (and drinking large amounts of coffee) so they can drag their 23-year-old selves to Slammers for the band's first post-jail, post-rehab show. This episode gets props for using "Working for the Weekend" in a montage.
The band returns in the final-season episode "Stuck in an Elevator" (first aired 7 Oct. 2016).