Gaara is the broly of Naruto, he is crazy op even as a baby. I think Gaara would pass the chunin exam at 4 or 5 years old. He has the ultimate defense and as well as the jinchuriki transformation. These basically curve stomp everyone other genin aside from Sasuke, Naruto, or rocklee. The only major obstacle would probably just be passing the written test at the beginning as he is 5 and probably can't think strategically enough to cheat.