The WHO recommends breast feeding till two years of age. However it is not advisable to have the baby feed in sleep or feed and sleep without cleaning the mouth. It can lead to cavities and other dental issues.

Till the age of 5 years..you can actually give. But that will be too long and difficult to break that habit later on. You can give for another a year or half. Now a days Paediatrician will say to give till 1 year. That will be sufficient. It depends on you. My gal still have at night. Shortly i will make her leave.