Password via category or via age of post

After 8 years (and some 1600-odd posts) I am changing my site and want to keep writing, but want to password protect all that I have written so far. I know I can go in and manually password protect each post, but that’s seriously onerous. Is there a plug-in to password protect via category, perhaps? Or anyone know of an easier way to go about this, like create a time sensitive plugin that passwords things older than x days? Thanks!