There's not a point when you know that one way or another. It's a gradual thing that begins to dawn on you, that telling stories is a special thing that people value and that you love to do. It's a matter of perception. Perception can be increased. It can also be decreased, which is why some writers fade with age.
Some people start off with a greater depth of perception of life and people than others.
All of this can be learned, but if you start from a very materialistic, mechanical view of life it is very hard to break through. Okay, so we're thinking big. Say I'm planning on being the next Maya Angelou. You write whatever you can to pay the bills, as long as it doesn't damage your spirit. That qualification is very important.