It's certainly not impossible. You'd be surprised at how many people do it all the time (I know some people personally who have done it).
You certainly need to be in bike shape to be sitting on a bike that long every day. And above that you should be in pretty good condition if you want to do it in a reasonable length of time.
If you're thinking about doing it, this is a good place to start:
http://www.adventurecycling.org/