Google’s head of search spam, Matt Cutts, posted a video yesterday answering why some old sites may not have their rankings in Google last forever.
Matt Cutts explained that there are many old sites that are in the range of about 15 years old and while that is a good thing, some of these sites have their original design templates and have not done much to their sites to improve things over the years. They have never redesigned the site, never updated the user interfaces, never added new features for their users, etc. If you want to stay competitive, Matt said you need to take a “fresh” look at your site and keep upgrading, tweaking, improving the site and the user experience.
Otherwise, new sites that have a better user experience, may surpass you, as they should. In short, having an old domain doesn’t mean you will always keep the rankings you have today, tomorrow.