Displays a message at the top of single posts published x years ago or earlier, informing about content that may be outdated.

This simple WordPress plugin displays a message in any single post that has been published x years ago from the current time or earlier. The default time to count back is 1 year, but you can change that.

• English (en_US) (default)
• German (de_DE)

If you don’t know how to install a plugin for WordPress, here’s how.

That’s because the plugin cannot know about what styles would match your theme, so it doesn’t apply any by default. You can add the default styles below to the style.css file of your active theme (child theme, preferably). If you’re not sure how to do that, you can alternatively use a plugin like Simple Custom CSS, or the Custom CSS module of Jetpack.

/* Default styles */
.aged-content-message {
	background: #f7f7f7;
	border-left: 5px solid #f39c12;
	/* Sorry, cheating here.
	   It’s Museo Slab on the screenshot. */
	font-family: "Georgia", sans-serif;
	font-size: .875rem;
	line-height: 1.5;
	margin: 1.5rem 0;
	padding: 1.5rem;
}
.aged-content-message hr {
	display: none;
}
.aged-content-message h5 {
	font-family: inherit;
	font-size: .8125rem;
	line-height: 2;
	margin: 0;
	text-transform: uppercase;
}
.aged-content-message p {
	margin-bottom: 0;
}

There is no settings page. You can customize the determination for post age, minimal age and, of course, the message itself via filters. Custom functions like these would go into the functions.php file of your active theme or—again—child theme:

/* Show message for posts aged 2 years or older. */
function yourprefix_aged_content_message__the_content_min_age() {
	return 2;
}
add_action( 'aged_content_message__the_content_min_age',
	'yourprefix_aged_content_message__the_content_min_age' );

/* Modify markup and wording of message (here: matching the value of 2 years set above). */
function yourprefix_aged_content_message__the_content_message() {
	return sprintf( '<div class="aged-content-message"><h3>%1$s</h3><p><em>%2$s</em></p></div>' . "\n",
		'Heads up! Content may be outdated.',
		'This post seems to be older than 2 years. It might not as accurate as it used to be.' );
}
add_action( 'aged_content_message__the_content_message',
	'yourprefix_aged_content_message__the_content_message' );

/* Set condition for displaying message to include pages. */
function yourprefix_aged_content_message__the_content_condition() {
	return ! is_single() && ! is_page();
}
add_action( 'aged_content_message__the_content_condition',
	'yourprefix_aged_content_message__the_content_condition' );

Honestly, I really felt it doesn’t need one, but it might get one in the future.

“The times, they are a-chagin’”: Message on a single post view informing about content that might be outdated. (Not diggin’ Bootsrap that much these days.)

• simplified calculation by introducing core constant YEAR_IN_SECONDS, props @sergejmueller

• Improved post aging calculation, props @2ndkauboy!

• Fixed minor formatting issues, props @bueltge!

• Fixed a broken link in readme.txt.

• Initial release.