Born in Copenhagen, Arentoft started playing football with Copenhagen club Brønshøj Boldklub. He made his Danish national team debut in June 1965, and played four national team games while at Brønshøj.
A Danish footballer from Copenhagen, Arentoft started his career with Brønshøj Boldklub's youth team before making his international debut for Denmark in June 1965. During his time with the club, he represented Denmark in four national team matches.