Age does affect a domain ranking in the Search Engine. This is because domain are so cheap this days that a lot of people could easily buy a big bulk and hope that some website actually makes it to the top of the search engine. Some even argue that if you register a domain with by paying more than a year, which means that the expiry date is much more further away, the credibility is also much better.

Of course there is no way to cheat or change the age of domain, but it is always easier to do search engine optimization on a domain that is existing rather than doing it from the scratch. But if you are already thinking of SEO when you purchase your domain, it does have a good advantage having the keyword in the domain.