Glossary Term: Document Age
Document age means the date the search engine crawled and indexed the page. Some people may mistaken document's age is when the page is available to public.
Search engine re-visit the indexed page from time to time. If the indexed page does not have enough quality information, it may be drop by the search engine. If a page been indexed by search engine for a long period of time, most likely the page has information that worth user to search for. Search engines usually give a higher score for the page that had been indexed for a longer period of time.