ROME — Pope Francis named 21 new cardinals Sunday, significantly increasing the size of the College of Cardinals and further cementing his mark on the group of prelates who will one day elect his successor. They include a man who will be the oldest cardinal — Monsignor Angelo Acerbi, a 99-year-old retired Vatican diplomat who was once held hostage for six weeks in Colombia by leftist guerrillas — and the youngest — the 44-year-old head of the Ukrainian Greek Catholic Church in Melbourne, Australia, Bishop Mykola Bychok, named in a nod to the ongoing war in Ukraine. The new cardinals will get their red hats at a ceremony, known as a consistory, on Dec.