Size of the bag may not mean much. Can you take a hold and milk some out? Some are starting to wean the calves at four months, and I am seriously considering it. Watch to see how often the calf is sucking. Four or five times a day is about average, I think. Is the calf eating hay, grain, grass a lot on his own? That is a good indicator of how close you are to weaning the calf. Don't depend on the calf to wean itself OR the cow to wean him... that usually only happens someplace other than Kansas if you know what I mean... lol.