Mozart's famous works were composed well after he was 12 years old. Mozart was a prodigy too, but the works we hear today were not the ones he composed prior to his teen years.
Did you see the segment where he took the Beethoven sonata he's been studying with his piano teacher (a concert pianist) and turned it upside down & played it? He mentally transposed the clefs, and played the music upside down & backwards! Didn't sound bad, either! The teacher was properly amazed.
Being a prodigy is helpful, but it does not mean that his compositions will be good. While Mozart was a prodigy, most great composers were not so gifted. They used hard work, re-writes, alcohol, prayer, and research to give the the world their beautiful gifts. Think Tchaikovsky, Brahms, Bach, Handel, Scubert, etc. etc.