Writers actually tend to be rather slow starters. You don't hear about a mathematician's "juvenilia", but a search on Amazon for "juvenilia" turns up quite a fe

Writers actually tend to be rather slow starters. You don't hear about a mathematician's "juvenilia", but a search on Amazon for "juvenilia" turns up quite a few--quite a lot of Jane Austen, but also Charlotte Bronte, W.H. Auden, and Leigh Hunt.