Find....

• Find and compress files older then X days

find /path/to/files/ -type file -mtime 1 -exec gzip {} \;

1 means 24 hours old

-1 means less than 24 hours old

+0 means more than 24 hours old

+1 means more than 48 hours old

• Find and compress files older then 5 days and exclude files already compressed (ext .gz)

find /path/to/files/ \( ! -name *.gz \) -type file -mtime +5 -exec gzip {} \;