Date Last Matched and NAS for Delete after X Days

I am trying to purge files off of a folder in a NAS after x days. The problem is that Date Added is not available on the NAS. From what I can see the only thing I have to work with reliably is Date Last Matched. I'm trying to determine if there is any way I can set up a rule that will match after x days ... the problem being that if it never matched, it passes a not in the last ... rule and deletes the file right away.
Open to any other way of solving this problem as well
Open to any other way of solving this problem as well