Many times bloggers will hide the publish date of a blog post. You can find the date using these tips and tricks.
Disclaimer: the post used as an example here was picked at random. There is no right or wrong answer to whether you should publicly display the publish date of your own blog posts.
To get an idea of the age of a post, add the URL at the end of this string [not an exact pub date but an indication that the post is older] http://web.archive.org/web/*/
This strategy usually works but there is a chance the post image was changed at some point. When in doubt use WASP (see #2) if there are multiple post images.