The 19-year-old Italian forward has scored four goals in six Serie A appearances for the Rossoneri, with a further strike in the Champions League.
"Finally, something happens," Evani told Tuttosport. "There is more confidence now in the quality of [young players], which is not lacking.
"You just need more courage to take risks, and we can work harder because you have to start from the bottom. However, I think it will be a quality [Milan] derby [against Inter Milan on Sunday], as usual.
"I like [what] Milan are doing, without giving too much prominence. Stephan is intelligent, and has undoubted quality but [he] should know that you can always improve and that you can not lie still in football, in a moment [you can] lose everything."
Evani played for Milan from 1980 to 1993.