Yes, site age is far more important then domain age. Because they are established with many backlinks.
Google certainly takes into consideration the age of a domain when determining it's listing (as well as its PR), think about it would you rather give a top level spot to a site that has been around for years, with thousands of backlinks and content, or to a site that just turned up yesterday regardless of the number of links?
Old websites are a sign of reliability & consistency and hence, it does get some weightage in ranking.