Wolfgang Mozart's father, Leopold Mozart, has taken no small amount of flak for capitalizing on his children's musical gifts. Musicologist Maynard Solomon points out in his biography of Mozart that Leopold Mozart's letters reveal a man urgently aware that child prodigies sell, but older musicians not so much. In 1766, when Wolfgang Mozart was 10 years old and his older sister, Nannerl, had reached 15, Leopold wrote to Mozart family friend Lorenz Hagenauer, "Surely you will agree now is the time when my children on account of their youth can arouse the admiration of everyone." Two years later, Leopold wrote to Hagenauer, "Should I perhaps ⦠let Wolfgang grow up, and allow myself and my children to be made fools of ⦠until he [Wolfgang] attains the age and physical size that no longer attract admiration for his merits?"