Complex sentence: He started an a cappella singing group with Michelle Baughan and Rikki called Three People when he was seventeen and sang with Rikki's group Boysie on and off for several years.
Split into simpler sentences: He started an a cappella singing group with Michelle Baughan and Rikki called Three People when he was seventeen. He also sang with Boysie, a band Rikki started on and off for several years.