Age of opportunity or date range to trigger alert.

Age of opportunity or date range to trigger alert.

We want to set up an alert when an opportunity is older than 45 days and status is proposal.  I cannot seem to get an "age" for the opportunity or set a rule to trigger 45 days after create date and status = "proposal".

I hope this is clear, can someone help? or suggest a workaround, many thanks.

SEAN.