Talk with your child's doctor/nurse practitioner. I think the more important question would be when to change from formula to whole milk. Infants need fat in their diet to assist their nervous system to develop during the first few years of life. So make sure your baby gets the nutrition they need! They often want to be like everyone else and use a cup when they are ready. Not letting them fall asleep with a bottle in their mouth is another issue...can cause ear infections and tooth decay among other things!