Once again, Miss B. is the voice of wisdom.
I breastfed my daughter until she was 3 1/2, never once while we were both standing with her on a stool, though.
It is the norm in other cultures to breastfeed until 3-4 years of age and is life saving in many cases because of lack of sanitation and poor nutrition.
I will disagree with the notion that older children (beyond 4) are being encouraged by the mother to continue. The mothers I've known that are breastfeeding at that point are actively working on weaning, and oftentimes the children have special needs.