I am 64 and have been a vegan for six years. I was recommended to adopt the diet by a naturopath whom I consulted for a serious complaint following diagnosis by a GP, for which an operation was prescribed. However I did not need one and also have now rid myself of several minor ailments such as coughs, colds, sore throats, etc. I am therefore a convinced advocate of veganism from the health point of view.
Purely by chance (and I would not do so now by my own choice) I have worked for some time on a small dairy farm. I firmly believe that dairy produce is not only unnecessary but positively harmful as an item of diet. I do not think there is much cruelty involved on an old-fashioned mixed family farm, indeed a cow chewing the cud in a spring meadow is a picture of health and contentment. But intensive rearing of calves for veal is of course extremely cruel and bulls are often kept confined and tethered throughout their lives.
As for the ethics of such a way of life, I have lived and worked in the countryside on farms, gardens and woodland for 34 years (the first three of which were spent in what is now called self-sufficiency) and I have come to the conclusion that Darwin's theory applies to human beings as well as plants and animals - ie, that life is a perpetual struggle to survive, and that one must battle with the elements and other forms of life in order to do so. The idea of perpetual peace and harmony does not seem to apply in nature - carnivorous animals destroy others, plants suffocate each other, and human beings, who are far too numerous for the space available, periodically slaughter each other, in competition for the natural resources of the earth.
This might seem a somewhat gloomy view of things. However I think we are now entering the post-industrial era, and the industrial revolution which has been an absolute disaster is about to be put into reverse by sheer force of circumstances, ie the depletion of sources of energy. It is up to each one of us to adapt to this situation and I think veganism is the way to do it.