Can I protect content AFTER X days? Reverse drip content?

Hi, I'm looking to have a few several membership levels for protected content that allow for only NEW content to be available to those members, while protecting the archive (18 months and older) from everyone except an unlimited membership. In other words, member group A would see everything, member group B would see everything newer than 18 months old, and non members would only see unprotected content. It's basically a reverse drip.

Ideally, the 18 months would be a floating limit, dynamically locking content every day.