This plugin labels old posts on a wordpress website. This is useful if you have older posts that you may want to remind the user about information possibly being out of date.

Install the plugin. Then, insert the following PHP in your theme file that is used for posts. This may be called content.php

do_action('label-old-posts');

The message will be included in a div with the class of label-old-posts-label. Target it with this CSS selector:

.label-old-posts-label

Download dist/label-old-posts.php and upload to your plugin directory - or visit https://wordpress.org/plugins/label-old-posts/ to see the official distribution.