How old was Mother Teresa when she decided she wanted to work with the poor? Agnes Gonxha Bojaxhiu was only 12 years old when she decided she would become a missionary and help the poor. Her parents had taught her that it was important to give food and care to anyone who asked for it. When she became a nun, her name changed to Mother Teresa. She chose the name Teresa in honor of Saint Thérèse, the patron saint of missionaries. Mother Teresa's Missionaries of Charity served Hindus, Muslims, Protestants, atheists, and anyone else who needed their help. Her missionaries have set up more than 500 homes for the poor around the world.