What age did Wolfgang Amadeus Mozart start playing the violin?

Beethoven was a virtuoso pianist, and wrote much of his early music for his own performances. He was also instructed by a relative in playing the violin and viola. From age 7 to about 9 his father tried to exploit him as a Wunderkind, as Mozart's father had done with Wolfgang. It is not clear whether he performed on violin or only on piano during those appearances, and by age 9 they were over.