#!/bin/sh

find . -maxdepth 1 | grep -v ^.$ \
    | while read file
do 
    date="$(stat -f "%Sm" -t %Y-%m  "$file" )"
    [ OLD-$date ] && mkdir -p OLD-$date
    [ "$file" != "./OLD-$date" ] \
        && mv "$file" OLD-$date/
done
echo done.