This is a straightforward problem but we can't give you an actual formula without knowing where all your data is. Can you attach a file with some sample data? It appears that you do not have the age as data, so the first thing I would do is add a column that gives the age as current date - due date.

The paper clip icon does not work for attachments. To attach a file, under the text box where you type your reply click the Go Advanced button. On the next screen scroll down and click on Manage Attachments, which will show a pop-up window to Select and Upload a file. Then close the window.