It took Tolkien 12 years to write LotR (one book split into 3 (which are then 2 each)) and the Silmarilion). That's about 6 years each. We aren't at 6 years yet and finally, GRRM himself has said the book is ready to be published. This hasn't happened yet. He has said it should be done soon at a given pace or that it is close but HE has set a date for it.

in response to the big whiner:

6 years is a long time for us to wait but is very reasonable given what he is trying to do. Not only is he writing a book of such a massive size but he has created an entire world (not just a single continent) with so many different intermingling plots and narratives that have to mesh together not just to tell one story but in such a way that it fits the timeline he has set out. Don't forget about how he decided not to do a 3 year time jump (would have been cool) so that kind of put a wrench into things.