Been working on my 80,000-word novel for about seven years. I keep thinking I'm on my final edit, but then there's another and another. Csorensen makes a good point about the value of considering how many hours it's taken rather than how much time in years, months, etc. There have been weeks, even months, when I haven't worked on the novel. I've been putting a lot of time into it over the past several months, though, and it looks like I'll be done in a couple of weeks. I got to "the end" the first time after about three years.
Something I've learned, and that I'll apply to the next one, is to resist the urge to edit as I go along. (Well, to resist it some.) It's okay to leave known imperfections and keep going. They can be improved later. But that might not be needed because portions get edited out. There are portions I've spent considerable time on, polishing them up nice and shiny; then I've realized that they don't fit into the entire story well enough, and I've had to chop them. Seems the process will be more fun/less tedious to keep going past the mistakes. And in the long run, it will save time to wait to polish until later in the game, when there's a better idea of what portions will be kept.