The Google Cache date is the date Google last indexed or reindexed the page, it is not the date Google last crawled the page. Google has told us before, Google does not update the date of a page’s cache each time it crawls and the date has no meaning around your crawl rate – it is simply the last time Google has indexed or reindexed that specific page.

Gary Illyes from Google said so on Twitter, he said:

Here is a screen shot of the date:

Here is Gary’s tweet:

Older pages do not need to be reindexed all the time if the content on the page has not changed.

Forum discussion at Twitter.