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The hosts file on Windows is normally protected. Are you running as admin? Have you tried checking the attributes of the hosts file, is it ReadOnly, Hidden, System?

I periodically download the latest nightly build of ffmpeg from this url: https://github.com/BtbN/FFmpeg-Builds/releases The downloaded file is "ffmpeg-master-latest-win64-gpl.zip". The structure of the zip file looks like: ffmpeg-master-latest-win64-gpl .........bin ..............ffprobe.exe .........

Okay, I'm curious. What exactly is the point of all this? Why are you using wmic to simply run cmd.exe ?

You could always just reformat the external USB drive to NTFS.

This is one of those situations where I would use the unix like tools found in Cygwin. There is an excellent discussion of this exact topic "How to find and delete files older than specific days in unix?" at https://unix.stackexchange.com/questions/155184/how-to-find-and-delete-files-older-than-spec...