It is possible to become lactose sensitive at any age. The classic we used to see were World War II soldiers who often went months without consuming dairy products returning home and finding they could not longer tolerate these (my father was one of these men).
Lactase appears to be a rather delicate enzyme for some.
Your husband may be at the point where he needs to have these hemorrhoids medically treated so that he can have bowel movement without this pain and bleeding. This can involve surgical removal of these or injection to shrink them.