One study found average breastmilk intake to be 30 oz per day at 7 months and 19 oz at 11-16 months.
Several studies have measured breastmilk intake for babies between 12 and 24 months and found typical amounts to be 14-19 oz per day. Studies looking at breastmilk intake between 24 and 36 months have found typical amounts to be 10-12 oz per day. (http://www.kellymom.com/bf/pumping/milkcalc.html)