Find the Date - Archived Info
Archival databases like archive.org preserve copies of Webpages. Looking for archived copies can be a guide to the age of information.
For example, the page modified information for the example page shows it was last modified in 2009. Go to archive.org and paste the URL of this page in the WayBackMachine. Locate the oldest copy of the page there and paste that date in the box below. Example Page