Tyler Tork

Like blog posts, a Page can have an “Excerpt” field to override the automatic excerpt of 55 words from the beginning of the content. However, many themes don’t display this field when editing pages, so you can’t edit it.
This extremely simple plugin forces page excerpt capability “on”. The Page excerpt is visible in internal search results and “Query Loop” blocks, as well as in the output of many plugins (e.g. CC Child Pages). So I generally do want to decide for myself whether to accept the default excerpt.

Torknado Page Excerpt

Pages, like Posts, can have an Excerpt field to override the automatic "first 55 words" excerpt. However, many themes don't enable edit …

J0SiE

Created to help those people who don’t like to edit code in template files (or are too lazy to do that). 
Just activate the plugin and it will automatically show the_excerpts in your homepage, archives and search results. 
It tries to display your custom excerpt text and if it doesn’t find it it will show an automatically generated excerpt. 
You can also define excerpt length, custom read more link and attach a thumbnail.

Auto Excerpt everywhere

Thanks to author for creating this plugin. 
It's works out of box. And working fine at WordPress Version 4.6.1


Works out of the box on WP Version 4.6.1

The plugin automatically displays excerpts instead of full post contents in your blog. Custom excerpts and generated excerpts supported.

Torknado Page Excerpt vs Auto Excerpt everywhere