I think a lot of it depends a lot on where you are when you decide to start. I didn’t have any writing experience, other than taking a couple of writing courses in college, when I decided I wanted to tell “my story.” Whereas some people are getting MFAs at that point.
You also have to have a clear understanding of your focus. At one point I realized mine was too broad. If you have credentials in a field or a unique experience, I think people are able to move more quickly.
I’ve switched focus a couple of times, and in the process, feel like I have been improving my writing skills and hope I am gaining enough experience and knowledge to have something that people will think is worth reading.