In short, you have to create a new author with filled in bio and atleast one post assigned. If it is single person blog then also you have to create a new author, you may assign any old post. This is the requirement currently but we might change this behavior in the upcoming versions.
It would be very helpful and would appreciate it if you showed the author page at the end of a blog post even if a blog/site has only one author. I would hate to create another user and assigning a post to them just for the sake of it. Thank you.