If you have completed high school, university or college why haven't you authored a book yet. If you are underemployed then you should really think about authoring books. When I was in college I authored 17 books before leaving. I also self published an 90 minute long album of video game music before I left as well.
You can author as many books as you like. You can learn new skills by going through the motions of creating something and selling it. Chances are you learned none of those skills in your entire school career. But remember all of those essays you wrote? Why not use all of those skills to write a book or 12.
One thing that is clear about finding a job in this current state especially if you are young is that you have to take what you know and apply it usually in a different way. So what are you waiting for. Find a topic and get started. There is no excuse not to start.