In a Middle Grade book, the main character is looking out at the world, trying to figure it out. In a Young Adult book, he is trying to figure himself out, looking inward and trying to find his place or identity.
I think that is brilliant! If you are struggling to decide if your approach is cutting it as a MG or YA story, take a minute to consider what your MC is going through. How does he see the world? Where is his deepest struggle? Against the world or against himself? (maybe a little of both)