Hm, seems that this Yu Jin has some significant backing. An interesting choice, and does make for more unique storytelling.
Historically, he wasn't really known to have fought against the Yellow Turbans, and only started seeing action as a volunteer soldier for the Han shortly before Dong Zhuo's usurpation of the throne. He rose to a relatively significant local standing through his efforts, and marched under a military officer named Bao Xin, who was the local commander at the time.
Eventually, during the campaign against Dong Zhuo, and the subsequent quellings of Yellow Turban remnants, Bao Xin joined Cao Cao, who became the Provincial Inspector through Xin's advice.
Unfortunately, Bao Xin was killed during the final battle against the remnant Turbans, and his unit, which included Yu Jin, was reshuffled into another commander's. This commander, recognizing Yu Jin's talent, recommended that Cao Cao interview him directly. Impressed by Yu Jin, Cao Cao promoted him into his own personal army.