Born in Port of Spain, Trinidad and Tobago, Ros' mother was an African-Venezuelan; his father was Scottish. Ros' parents separated not long after he was born, and he was enrolled into a military school, where he became interested in music and learned to play the euphonium or bombardin. From 1927 to 1937 his family lived in Caracas, Venezuela. He played in a military band for four years. Later, he received a music scholarship from the government.