The son of a high school football coach, Gilbertson grew up in Snohomish, Washington, northeast of Seattle. He graduated from Snohomish High School in 1966 and attended Central Washington University in Ellensburg, Columbia Basin College, the University of Hawaii, and returned to Central Washington, where he received a bachelor's degree in social sciences in 1971. He later earned a degree in education from Western Washington University in 1974.