The new recommendations from the American Academy of Pediatrics for feeding food are 6 months. They recommend that babies are exclusively fed breastmilk for the first 6 months with no supplemental feedings (would include juice). You should try to breastfeedfor 12 months but if you are unable to you need to give formula. Babies need formula or breastmilk throughout the first year as the baby needs the nutrients for optimum growth. They will not get all the fat and calories they need through juice, water, and food during that first year.
Most daycare centers take babies starting at 6 weeks of age.