According to Wikipedia, it took nearly 10 years for writer/director Christopher Nolan to bring Inception to the big screen. He wrote the idea for Inception in 2001 but didn't think he was ready to tackle such a large project at that stage in his career, so he waited until 2009 before revising the script and selling it to Warner Bros.
At first I thought it must have been agony for him to wait that long to do his "dream" project (har) but actually... nine years is not that long. And it's not like he was idle all that time (ahem, Insomnia, The Prestige, Batman franchise), just biding his time and learning how to direct projects that were bigger in scale than his mind-bending feature debut, Memento. I think it was smart of him to wait, and rather inspiring.
Depending on what you're writing, nine years of development is not unheard of, especially with historical fiction. Let's say it takes a year to research, brainstorm, and jot down notes for your novel; two years to write the first draft; one year to revise based on notes from family and friends; six more months to revise based on agent notes; six months on submission; another year or two to revise for the editor; and one more year before it's actually published -- BAM! Eight or nine years, in a blink.
The trick is that it wouldn't be the only thing you're working on, of course. You could have three or four projects in the wings, at various stages of development, until before you know it, you've built a repertoire. And with each project, the process is streamlined to go faster. Some projects would only take a year or two.
That's what I choose to take from it, anyway :)