Terry Chay

<a href="http://terrychay.com/wordpress-plugins/blog-birthday" rel="nofollow ugc">Plugin Homepage</a>
Inspired by @TwBirthday on Twitter, this shows a simple message in the admin panel on 
their blog birthday.
“Happy 3rd Blogger Birthday! You’ve been around since 11 August 2008.”
“Happy 7th Blog Birthday! The first post on this blog was on 19 November 2004.”
“Happy 1st Blog Birthday! This blog was first registered on 23 July 2010.”
Caveats: 
– Old WordPress admin accounts have a registration date of 0000-00-00 and never have a 
 blogger birthday. 
– Blog registration starts when you turn on WordPress multisite. If you did this, the 
 date may be off. 
– First post assumes that there a post_id=1 and uses the date off that.
<h3>Future Features</h3>
<ul>
<li>Add ability to change the blogger birthday if blank</li>
<li>Add ability to change the blog registration date if first post is different.</li>
<li>4567890012345678900123456789001234567890012345678900123456789001234567890012345678900</li>
</ul>

Blog Birthday

Show a user a notification on their blog birthday.

kenkeydev

ACF Field to select a date with select drop downs rather than the typical popup date picker. Very useful for selecting Age/Date of Birth.
<h4>Compatibility</h4>
This ACF field type is compatible with: 
* ACF 5

Advanced Custom Fields: Date Selector

This was the perfect starting point for me to implement into a project. Saved a lot of time. For my clients use case we wanted to record dates of birth but the date picker calendar was confusing for users, and fiddly on mobile. This is a much cleaner solution.

A good alternative to the clumsy date picker

ACF Field to select a date with select drop downs rather than the typical popup date picker. Very useful for selecting Age/Date of Birth.

Blog Birthday vs Advanced Custom Fields: Date Selector