 Upon reaching the age of 80 on 23 September 1972, he lost the right to participate in any future papal conclaves, an opportunity which he never received.The Cardinal resigned as Paderborn's archbishop on 30 June 1973, after thirty-one years of service.A dedicated ecumenist, Jäger founded the Johann Adam Möhler Ecumenical Institute (named after the German theologian) and helped establish, along with Augustin Bea, the Secretariat for Promoting Christian Unity in the Roman Curia.