Actually, other animals do still drink milk when it is available to them. The milk cow we have been talking about , has to be bred each year to continue producing milk. Her calf is usually taken away after a few days, once the colostrum is gone. Some dairies actually just get rid of the calf, which is terrible, in my opinion. But anyway, if the cow was not bred back for a calf the next year, and her calf was left with her, it would continue to nurse way past the time it should have been weaned, and until the milk dries up and it can’t nurse anymore. I had a friend whose horse had a colt, and that colt was still nursing when he was over 2 years old. No one had separated him from his mother, and he just continued to nurse. We had milk delivery in the town where I grew up, but we didn’t get milk that way. My folks had a small grocery store, so our milk came via a grocery delivery truck, and had things like ice cream, cottage cheese, and other dairy products. The milk came in quarts, not gallons like we see now, and there were two choices, homogenized and pasteurized. If you got the pasteurized, it still had cream on the top, and you had to shake it before using it. As a side note, even at age 76, and not having had fresh whole milk in many years, I still shake my carton of milk before I put some on my cereal or in my coffee. Yes, I do know that it is super-homogenized, and most of the cream is already gone, but I still do it anyway. I had milk cows after I was grown, married, and lived in a place where I could have a milk cow (or milk goat), and I totally LOVE the taste of fresh raw whole milk. I also enjoyed milking the cow, squirting some at the cats (who always sat around waiting for that), and having fresh real cream in my morning coffee.
Interesting. I [obviously] did not know that some mammals continued to nurse to those ages, although now that you mention it, I can think of a couple of instances I've seen of children nursing at the age of 4-5 years old, since they did not get cut off. I one lived in front of a small 4H farm and have been around those scaled-down dairy activities, but have never lived on or near any dairy farms.