Born in San Jose, California in 1955, Castro first picked up a guitar at age 10. He came under the spell of Eric Clapton, Elvin Bishop, Mike Bloomfield and other blues rock players early on. As he got older, Castro moved forward by investigating the past, falling in love with the blues guitar work of Muddy Waters, B.B. King, Freddie King, Buddy Guy, Elmore James and singers like Ray Charles, Wilson Pickett and James Brown. By his late 20s he was playing in a variety of San Francisco-area blues and soul bands.