From the breast Feeding article in the Times
It has been estimated that a natural weaning age for humans is between two and seven years. Family physicians should be knowledgeable regarding the ongoing benefits to the child of extended breastfeeding, including continued immune protection, better social adjustment and having a sustainable food source in times of emergency. The longer women breastfeed, the greater the decrease in their risk of breast cancer. There is no evidence that extended breastfeeding is harmful to mother or child.
Read more: Breast-Feeding Older Children: How Weird or Normal Is It? | Healthland | TIME.com
I can understand if you're from a third world country, the benefit of extended breast feeding is acceptable.
I question the points bolded for people in North America and Western Europe. The majority of the people are well off (above poverty) so, breast feeding as a source in times of emergency makes no sense. The WHO also said that the age to breast feed could go out to 7 years old. I find that way too old. I also don't see how extended breast feeding is better for the child socially.