There is a published date that is reflected with every URL in Content Explorer.
Ahrefs determines this published date from a few of sources and picks the one that gives us the earliest date.
Here are some of the sources:
URL First Seen Date - this is when our crawler first saw the URL (not necessarily crawled it though)
HTML Markup - we recognize HTML tags like this one: <meta name=
"publish_date" content="2017-01-05T00:00:00Z"> and other similar tags
Archive.org - we check for when the page was first indexed