How Long Does it Take to Write a Novel?

This is a good question. It's a solid, straight to the point question about writing. It's a question that I've been asked quite a bit lately.

How long does it take to write a novel?

I've heard answers from it takes a lifetime to however long it takes you to read a book times five hundred. These responses make me laugh and are honest, but sometimes the length of writing a novel basically depends on what the writer really wants to do. Does the writer really want to write and finish a novel or no...