The Rossoneri have taken just seven points from their opening six games, including their first two home fixtures against Sampdoria and Atalanta.
"I think fundamentally our problems revolved around a lack of experience," Football Italia has quoted the Dutchman as saying.
"This is a very young side and many players were on the bench last season only to be promoted to the first team. It is never easy to change your perspective at a club like Milan.
"We lost to Sampdoria and Atalanta, but with all due respect, I think the only difference between us in those games was experience and cynicism. We're a new group and are improving game by game."
Two wins in the last three games has gone some way to steadying the ship at the San Siro ahead of tonight's crucial Milan derby.
De Jong, who joined Milan from Manchester City before the close of the summer transfer window, believes that the match will be won by the team that controls the midfield.
"Where can we win the derby? In midfield, like with every big game," he added. "Usually if you take control in the middle of the park, then you can have the better of the match."
Milan won their previous game 3-2 against Zenit St Petersburg in the Champions League.