He was born in Bergen as the son of Frithjof Sælen (1892–1975) and Astrid Weltzin (1892–1978). His father was an accomplished gymnast, with an Olympic gold medal from 1912. Sælen Jr. was a swimmer during his youth. He took the examen artium in 1937, studied one year at commerce school and then moved to Oslo to study drawing and advertising.