I haven't used this tool, to test your query I will have to test it in my lab.
As you already have this tool handy, could you try these parameters. In the XCP docmentation, they have given few examples for 3 months, but I am sure you could change that.
Try these :
scans all files that have not been modified for more than 5 months
C:\XCP> xcp scan -match "modified > 5*month"
If you also want to filter by certain size, say bigger than 4MB
C:\XCP> xcp scan -match "modified > 5*month and size > 4194304"
For complete command: