Find how much space emails over X days old are taking up for all users

I am in need of a few more ways to justify email retention policies to our organization. So far I have a script that shows the amount of email in each folder for each user and so on. I think it would help my case to show where our 2tb of email would be under different retention policies.

I was thinking about breaking it down by data store and going from there but after looking around I am not quite sure where to start.  End result would be to show how many gigs of sent email in the organization is over 60 days old and so forth... Any input is appreciated.