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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.
I've seen books with 3 chapters and others with 40. Unless you've already started a book before now, and plan on finishing that one, then (I don't mean to sound rude) then the possibility's of that becoming actually published in a years time isn't that likely.