To calculate the difference you just need to perform a subtraction, for example:
sysdate – some_date_column
The result will be given in days, so you have to convert it as needed.
To send the e-mail, you could use the UTL_SMTP database package, or write some forms code to use outlook to send it.
<a href=”http://www.dba-oracle.com/t_utl_smtp_utility.htm”>Oracle utl_smtp utility to sending e-mail</a>
<a href=”http://www.lazydba.com/oracle/0__113257.html”>Forms – Emailing via Outlook </a>