Many of the nuns started teaching right out of the novitiate. They were about 20 years old and were put in a classroom with 50 kids. At night they went to school earn their college degrees and learn how to be a teacher. Many years later, at a high school reunion, I discovered that one of my high school classmates was the brother of the nun who taught me in the fifth grade. He told me how old she was. She was 21 years old when she taught me and she was in her second year of teaching. She taught us how to diagram sentences.
Thank you for the post and ping. It crossed my post #6 that I think you will appreciate. When you get the chance, please read it.