Trying to create an average formula without creating multiple columns

Hello,

I am trying to create an array formula that will give me the average of two dates, one of which is the current date. Basically, I need the following under certain conditions:
Average Number of Days Since Created = (Today’s date – created date) / number of records if status is “In Progress”

I have tried to put together a number of different arrays but cannot get anything to produce the proper results. I feel like it would look something like this, but this doesn’t work: if column 1 = “criteria” then subtract the value in column 2 from a constant value and take the average of all of the differences within the range.

Example:

Column 1 Column 2 Column 3 Column 4
Jack 3/1/2013 Yes 5
Jack 2/28/2013 Yes 2
Jack 2/26/2013 Yes 3
Jack 2/25/2013 No 6
Jack 2/6/2013 No 9
Casey 3/1/2013 No 8
Casey 3/3/2013 No 4
Casey 2/28/2013 No 2
Melissa 3/4/2013 Yes 5
Thomas 3/5/2013 Yes 9
Thomas 2/6/2013 Yes 4
Thomas 2/26/2013 Yes 7
Thomas 2/25/2013 No 7

What can I write that would take the information in column 2, subject it from the current date, and average the difference of all of the values in the data set? I’d rather do this than create a new column with the difference and then just taking the average of that column.

Any help anyone can provide would be great!
Thanks!