Yes it was true in both China and Malaysia in the olden days many old men who were already in their death bed were given a longer lease of life after drinking (confinement period) breast milk. Usually family members would even go around looking for the first born's breast milk which was considered the best for an ailing elder. I had even heard that the procured milk was prayed over by the temple monks to give it a better curative power.
According to one of my aunts, one woman who sold her "first" milk in this way earned enough to buy all her chickens for her confinement. Her mother in law was very happy about the whole situation as they were facing financial difficulties. However her first born was slightly malnourished as a result and was sickly throughout her life. One cannot have the best of both worlds.
The Foochow pioners practised Wet Nursing in the olden days. Wet nurses were hired and had to live with the family as servants, not just for a month but for as long as the wealthy family could afford it. thus a wet nurse could even stay up to three years or more. Most lactating women would not mind making a bit of money from sharing their breast milk with women who were not lactating well. It was also a part of their community service while getting a small ang pow (or token) helped ease family financial situation.
A local Miri coffee shop owner now in his 70's said that many Foochow women in Sarikei helped each other in breast milk supply very willingly. There was so little money around and tinned milk powder was not at all available in the 20's or 30's. In the rural areas like Ba Te Li and Murudu, the abject poverty of the farmers led to women helping women in order to raise their babies. In fact he even knew of a few babies who died from illnesses. He said his own mother had enough breast milk to give away to help others. He related this story very emotionally.
Many strong farmers' wives made good wet nurses and in fact their husbands found it a rather lucrative business for the family to farm their lactating wives out. The extra income was very much welcome in the cash strapped days of Sibu in the 1930's.
Usually a rich man would send word out to the villages to "book" a pregnant farmer's wife who would deliver about the same time as his wife. When the rich man'swife delivered, the wet nurse would come to the house and nurse the baby while the rich man's wife enjoyed her very luxurious confinement life.
Sometimes the wet nurse had enough milk for both babies and it was well and good. Sometimes she only had enough milk for the child of the rich family. The wealthy family would allow the wet nurse to look after her own child as well as the "rich baby".
The two babies would thus grow up together, knowing about the sharing of the milk. The rich man's son would respect the wet nurse as Milk Mother. A story was told to us that one rich rubber garden owner had a son and at the last minute had to book a wet nurse when his wife was taken ill with asthma before she gave birth to her baby boy. Her previous delivery, a baby girl, had resulted in an early infant death. The desperate rich man could not find any one but his own sister in law who was willing to help.
The sister in law gave her milk to the first born son of the prestigious family while her own child, a girl, was fed on rice water. Most of the relatives know that the eldest son of this family lived up to almost 100 years because of "the milk from an aunt the wet nurse" while the cousin had a short life.
The villagers would always mention in those long ago days how beneficial it was to have mother's milk.
I believe many of our grandmothers were "farmed out" as wet nurses when times were bad.
In addition, wet nursing is actually quite universal and is not just a Chinese cultural practice.
See this : http://www.nwhm.org/blog/2010/06/ (The Evolution of Nursing)