Sarah was 90 years old when Yitzchak (Isaac) was born. Sarah died at the same time as the Akeidas Yitzchak (Binding of Isaac). Sarah was 127 when she died [Bereishis (Genesis) 17:17, 23:1]. How old was Yitzchak at the time of the Akeida?
127 years – 90 years = 37 years