old post flagging

I have about 2000 posts going back to 2003, and the usual problems that come with a weblog this size. There used to be a plugin that put a flag at the top of any post older than xxxx. Mine said: This was first posted in xxxx. Some or all links may no longer work.

The plugin still exists but hasn’t been updated in two-plus years. Is there another way to do this?

Thanks for any help you may be able to provide.