Complex sentence: Riabko has been performing since the age of 10 and began his international music career during his junior year of high school when he toured with John Mayer, Buddy Guy, and Jason Mraz, among others.
Split into simpler sentences: Riabko has been performing since the age of 10. He began his international music career during his junior year of high school when he toured with John Mayer, Buddy Guy, and Jason Mraz, among others.