find . -ctime -7 -type f -name "*.csv"
This will list the files with .csv extension that have been created during the last seven days.
If you want to use the above to tar them up you could use something like this:
tar cfz `date +%Y-week%V`.tar.gz `find . -ctime -7 -type f -name "*.csv"`
(note the backticks for command substitution)This will create a compressed tar file with the csv files created during the last 7 days, and the filename will be YYYY-weekN.tar.gz (currently it would be 2004-week18.tar.gz). Try man date
for more options on formatting date output.