Bill Erickson

When editing a post, check “Mark as Old” in the metabox labeled “Old Post Notification” to add the notification to the top of the post. You can also define a custom message for this specific post. If no custom message is provided, the default message set in Settings > Old Post Notification will be used.
Further Customization with filters, described in documentation.
<a href="https://github.com/billerickson/old-post-notification/wiki" rel="nofollow ugc">Documentation</a> | <a href="https://github.com/billerickson/old-post-notification/issues" rel="nofollow ugc">Support Forum</a>

Old Post Notification

Mark posts as old and display a notification message above the content.

nestwiderhaken

Shows only posts, that are newer, than the day the current logged in user was created. 
This plugin is only useful if you have an other plugin installed forcing any visitor to login first. 
In that combination you get a blog in which the posts of older users are invisible for new users. 
None of the old users must therefor worry about statements made in older posts becomming available to users he don’t want. 
In the moment a user publishes a post, the amount of authorized readers for this post stays the same.

Only New Posts

Works fine.

Shows only posts, that are newer than the day the current logged in user was created.

Old Post Notification vs Only New Posts