Is there a formula that I could use to average the times between a series of dates?

My worksheet has two columns, column A is a start date and column B is an end date.
I need to take the number of days between each start and end date to find the average
number of days between all of the start and end dates.
My table essentially looks like this:

Start Date End Date
1/1/01 1/4/01
1/7/01 1/9/01
1/10/01 1/15/01
1/17/01 1/18/01
1/20/01 1/26/01

While the dates above are pretty easy to count and average in my head, the sheet I am
working with has way more data; so I'm looking for an easier solution than mental math.
Thanks!