Complex sentence: Growing up, Vallely played little league baseball, but, in 1984, at age fourteen, Vallely discovered skateboarding and punk music, borrowing a skateboard from a friend and proceeded to dedicate his life to skateboarding.
Split into simpler sentences: Growing up, Vallely played little league baseball, but, in 1984, at age fourteen, Vallely discovered skateboarding and punk music. Following his interest in punk music, Vallely borrowed a skateboard from a friend and proceeded to dedicate his life to skateboarding.