J.B.
In other societies that are less.... technologically advanced... women often breastfeed until the child is 3-5 years old. Sometimes it's longer. A child's most complete form of nutrition will come from its mother.
I am personally conflicted about the inclusion of substitute milks in a childs diet. Cows milk and goats milk are fine- if they are raw. It is possible to find a provider of raw goat and cows milk. You should check out websites for local dairy farms in your area. Most reputable farms will have the milk tested rigorously for bacteria and other issues. It's important that the milk comes from "organic" cows/goats that are pasture raised and not treated with antibiotics and growth hormones. Pasteurization ruins some of the proteins. Nut and grain milks have their own issues. Soy inparticular is a bad choice because it is has an estrogenic effect on the body. Another issue with grain and nut milks are that they tend to come from GMO plants, and are chock-full of synthetic supplements that the body can't necessarily absorb.
Anyhow- if I had been able to breast feed my children longer than 5 months each (breast surgery) I would have fed them via breast for as long as they asked for it. It is the best way to give them the absolute strongest start in life- imo.
Best wishes!