@jan80 yes, that is in the development list and it will be implemented very soon. The reason why older cached .css/.js files aren’t deleted is that I wanted to make sure that cached pages or pages accessed via Google cache (on search results) will not be broken. I’ve seen it many times with other caching solutions. Once you clear the cache, they also delete the older CSS/JS and when I access those pages in Incognito mode or other browsers, they were broken. Not ideal for any visitor, especially first-time ones.
I agree that something has to be done and until a feature to manage/delete older files will be implemented, I suggest you use cPanel or Filezilla (any FTP client), sort the files by date and delete the ones that you believe are too old and not used in cached page anymore.
From what you’re saying, you have many users on your website as the way it works now, the plugin places the cached CSS/JS for every user (something more effective will come up) in its own folder based on the ID of the user. That was the easiest way to avoid too much PHP processing and memory usage, but it will be improved ??
If you have suggestions, let me know. I hope you enjoy using the plugin otherwise!