Complex sentence: He began playing at the early age of six after using a full-sized guitar with a shaved neck (to accommodate smaller hands), and was trained by, and at age 13, eventually toured with, B.B. King.
Split into simpler sentences: He began playing at the early age of six after using a full-sized guitar with a shaved neck (to accommodate smaller hands). Later he was trained by, and at age 13, eventually toured with, B.B. King.