In ancient India, influenced by the belief that the longer a child nursed the longer he would live, mothers usually nursed their children as long as possible, often seven or even nine years sometimes. In Tsinghai, China, mothers observed in 1956 were still nursing for several years, five years not being unusual, or until another child was born. In Inner Mongolia in 1951, children nursed two or three years, nor was it rare that a six- or seven-year-old would want to nurse for a bit of reassurance.
In europe, they did it to reduce the mother’s fertility. Some believe a lactating mother has a difficult time getting pregnant.
As late as the 1960s Inuit (Eskimo) women would nurse their children as long as possible, even into their twenties. They believed that as long as a woman could nurse, she proved she still was a vital, useful person. It was a symbol of femininity.
I never cease to be amazed at the variety of human societies and what the various cultures consider moral and normal.
As for me, I think breastfeeding is a natural, beautiful thing. However, I also think its odd past two or three years old.