Re4DeR

This plugin is very usefull if you want warn people going to one category.
It set cookie, co visitor will see alert message only once.
For example you have a magazine and in one category you have adult content. 
With this plugin you can set up warning for access to this category-and user have to confirm your message.
<h3>A brief Markdown Example</h3>
Ordered list:
<ol>
<li>Choose between alert and confirm</li>
</ol>

WP Warning

This plugin allow you warn visitors when they want to go in category.

Șerban

On every single post, older than 1 year (365 days), you may add a custom formatted text, in order to let your readers 
know the information included might be outdated.

Old Post Warning

This plugin will display a custom notification on every single post older than 1 year (365 days).

WP Warning vs Old Post Warning