Active/Inactive Authors

I’m trying to figure out a way to distinguish between active and inactive authors on my site and I’m wondering if there’s coding available that will allow that. Right now, when you hover over the “Authors” drop down menu in my nav bar, every person who’s ever posted on my site is listed. I don’t want to delete their accounts because you never know when they might be interested in posting again. On the other hand, I don’t want them listed in my “Authors” drop down menu if they haven’t posted for a while (let’s say 60 days).

Is there a way to add code that would allow me to specify a number of days before an author is listed as inactive and removed from the drop down menu?

Thanks in advance!

Mike