#delete directories older than 20 days and not older than 365 days
find /home/username/backup/ -type d -mtime +20 -mtime -365 -exec rm -rf {} \;
#delete pdf files older than 6 days but not older than 365 days
find /home/username/public_html/storage/ -type f -mtime +6 -mtime -365 -name '*.pdf' -exec rm {} \