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.