Rakesh Raja

This plugin hide content in posts and pages and display only when a user leaves comment. If page/post dont have a comment from user or its got deleated by admin, content will be not displayed.
This plugin uses cookie for that so this plugin will work when user allow website to set cookie.
Restrict it provides you a shortcode [wpgrestrict][/wpgrestrict], wrap your content with this shortcode and you are done.
In next version, I am going to to add restrict content by logged in user. Please let me know if you need any other way to restrict content.
<h3>Arbitrary section</h3>

Restrict It

Restrict content in posts and pages with this plugin and display only when a user leaves comment.

Chase Wiseman

Whatever your reasons, you may need your site’s visitors to confirm their age before viewing the content of your site. Age Verify does just that. It’s a simple plugin that lets you specify a minimum age and add an age-gate between a potential visitor and your content, just to be safe. Enjoy!

Age Verify

Like my review on another similar plugin, because this plugin uses PHP to check cookies, it doesn't work with cached pages...such as with the W3 Total Cache plugin or WP Engine.

Would be better with Javascript

A simple way to ask visitors for their age before viewing your content.

Restrict It vs Age Verify