 The young Mendelssohn was greatly influenced in his childhood by the music of Bach , Beethoven , and Mozart , traces of whom can be seen in the 12 early string symphonies , which were mainly written for performance in the Mendelssohn household and not published or publicly performed until long after his death . He wrote these from 1821 to 1823 , when he was between the ages of 12 and 14 . 
