How old do you have to be for a book contract?

[Julian]

Well, the manuscript is the novel itself. Everytihng you wrote, every piece of dialogue, the story, the book itself is the manuscript. And no, you don't have to be a specific age, some 6 year olds write poetry books. The contract is just the negotiations for the book and your publisher/agent. You can find overviews of contracts online. I think you have to have a parent or legal guardian grant permission for the book if your 'underage' if that's the term you want to use. You're never underaged to write. Never.