Performing Joins Between Sharepoint Lists

Yes you can! Thank you Sahil Malik!

Today - Created, or Today - Modified

Yes, it is that simple. In a sharepoint calculated column, AFTER you perform the [Today] Sharepoint trick - you can use Today - Created, or Today - Modified in a calculated column to display X days old. Don't forget to format the column as numeric with no decimal places as we are reminded here.