Passage: On Saturday May 12, 1944, Cash's older brother Jack, with whom he was close, was seriously injured in an accident at his job in a high school. He was pulled into an unguarded table saw while cutting oak into fence posts, and was almost cut in two. He died from his injuries a week later. Cash often spoke of the guilt he felt over this incident; according to Cash: The Autobiography, his father was away that morning, but Johnny, his mother, and even Jack himself, all had premonitions or a sense of foreboding about that day. His mother urged Jack to skip work and go fishing with his brother, but he insisted on working as the family needed the money. On his deathbed, Jack said he had visions of Heaven and angels. Decades later, Cash spoke of looking forward to meeting his brother in Heaven.Cash's early memories were dominated by gospel music and radio. Taught guitar by his mother and a childhood friend, Cash began playing and writing songs at the age of 12. When young, Cash had a high-tenor voice, before becoming a bass-baritone after his voice changed.In high school, he sang on a local radio station. Decades later, he released an album of traditional gospel songs, called My Mother's Hymn Book. He was also significantly influenced by traditional Irish music, which he heard performed weekly by Dennis Day on the Jack Benny radio program.

Question: At what age Cash start praciticing music?
12