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It's okay to publish a book at any age. If it is a good book (or at least good enough.) Worse come to worse, if you can't publish at age 13, you can try again at age 18 or age 23. A famous writer, Pearl S. Buck published her first book at age 10, I believe.
Using that, and the PW numbers, we come out that a handful of bestselling self-published authors will hit 300,000 copies per year, per title. Maybe a hundred of the rest will hit 30,000. They're usually publishing their books at about $4.99 per copy. And they get 70% of that, or $3.50.