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His music and music writing skills
Playing music/writing it, of course!
Mozart wrote his first opera when he was 12 years old. Becuse he was inspired by music.
Mozart's father introduced him to the pianoforte when he was four years old. Mozart began writing compositions when he was five years old. From then, he taught himself the violin, viola, and organ. Mozart also played the harpsichord. For more information, read this article: http://www.musicatschool.co.uk/year_9/Classical_sheets/Mozart.PDF
Mozart didn't write he composed music. So to answer your question the answer is zero or none.
One thing I know; he was barely 10!
At the age of three, it was apparent that Mozart was a musical prodigy and he was taught to play the harpsichord, violin, and organ by his father. More about Mozart can be found at - http://en.wikipedia.org/wiki/Wolfgang_Amadeus_Mozart
The famous composer that began composing at 5 was Mozart. He started learning to play instruments at the age of 3 because of his dad, who was also a musician. Then at 5, he composed his own music.
Mozart's father (Leopold Mozart) helped influence his music.
Mozart Composed Classical Music.
Mozart [1756 to 1791] Mozart wrote the Ave Verum in June 1791, six months before he died. He was 35 years of age. Had he lived, one wonders what other beautiful music he would have left us with. Marian Cooper
He is the person who catalogued Mozart's music. Hence Mozart's compositions are identified by K numbers.