Scott Nelle

WordPress lets you set a number of days after which comments will be unavailable for individual posts. This plugin will allow you to keep commenting open on specific posts.
Once the plugin is enabled:
<ul>
<li>Set a comment deadline in Settings > Discussion using the “Automatically Close Comments…” option. Closing comments on old posts is a great way to avoid spam comments.</li>
<li>Edit an individual post on which you’d like to keep discussion open indefinitely and check the Override Comment Deadline box.</li>
</ul>

Override Comment Deadline

Allows you to enable comments on posts which are older than the comment deadline set in discussion settings.

Seth Alling

Up until recently, WordPress gave two options: You could either disable comments and trackbacks by default for all pages and posts, or you could have them active by default. In WordPress version 4.3, this finally changed so comments are always disabled on new pages.
While the new change makes it easier for many of the sites, it make it harder for people who need to get the reverse and enable comments on all pages, or if they need to change the default for a custom post type. This plugin allows you to choose whether comments are enabled or disabled by default on all new posts, pages and custom post types, while still giving the ability to individually enable comments on posts or pages.
Also, this plugin provides a way to quickly disable all comments or pingbacks for a specific custom post type. It directly interacts with your database to modify the status, so it is highly recommended that you backup your database first. There shouldn’t be any issues using this feature, but it’s always good to play it safe.
<a href="https://github.com/sethta/no-page-comment" title="No Page Comment Development on Github" rel="nofollow ugc">View No Page Comment Development on Github</a>
<a href="https://github.com/sethta/no-page-comment/issues" title="Report an Issue about No Page Comment on Github" rel="nofollow ugc">Please Report any Issues about No Page Comment on Github</a>
<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=5WWP2EDSCAJR4" title="Donate to support the No Page Comment Plugin development" rel="nofollow ugc">Donate to Support No Page Comment Development</a>

No Page Comment

An admin interface to control the default comment and trackback settings on new posts, pages and custom post types.

Override Comment Deadline vs No Page Comment