One of the many factors in Google's search engine algorithm is the age of a domain name. In a small way, the age of a domain gives the appearance of longevity and therefore a higher relevancy score in Google.
The age of the website is built up of how long the content has been actually on the web, how long the site has been in promotion, and even the last time content was updated. The length of time a domain has been registered is measured by not only the actual date the domain was registered, but also how long it is registered for. Some domains only register for a year at a time, while others are registered for two, five, or even ten years.