My mother and father tried to have children for twenty years with no success. My father went to a doctor and they found no issues with him, so they assumed my mother was infertile and went on about life. Then, out of the blue, she got pregnant at age 41, and here I am.
Same thing happened to a friend of mine. The oldest I’ve ever heard of a woman getting preggo with her first baby (naturally) is 42. Maybe there are some older, but I haven’t heard of them.