Domain Age and Authority concepts that are widely spread in the SEO jargon and they are both correlated. The reason for this is that it is now Google´s policy that each new website has to show its value by providing original useful content to human readers and must be working on its link building structure for a minimum period of time.
While this period of time occurs the website is kept on what is known as the Sandbox and is not assigned any Page Rank. If after this minimum time period, improvements are observed within the website from Google´ s perspective then the site will be assigned a Page Rank and will head on the path towards higher rankings.