Juan Crisostomo Arriaga was called "The Spanish Mozart" because he was a composing prodigy and also died young. When we discuss child prodigies in this era, we tend to focus on early mathematical ability, early reading, and fluency in multiple languages. Those do seem amazing to me. Yet I can see those mountains from my own hill. I cannot in any wild stretch of imagination fathom a twelve-year-old writing this.
Those we call musical prodigies today are performers like Sungha Jung (who I love - don't get me wrong). Not even an arranger.