My DS was intolerant to dairy from birth. I had to cut all dairy from my diet while breast feeding because it caused him to vomit severely after every feed. I noticed an improvement from about 10 months. When he was 13 months I weaned him and from that point on he drank cow's milk and consumed dairy directly himself every day with no ill effects.
DS1 started growing out of it about 14m, able to eat cheese & yoghurt now. The dietician wanted us to challenge his other allergies before attempting liquid cows milk. Over the last 8m we've had success with gluten, wheat& soya, so I can imagine they'll want us to test out proper milk soon... Probably about 2yrs old by then. Just about to start the DF weaning all over again for DS2!
DS lactose intolerant from birth, he is almost five now. he can tolerate everything now except pure milk. We "tested" him at various points in last five years and always left it about 9-12 months before we tried again. At about 4 or 4.4 we noticed he could manage new foods previously off the menu though still not milk as yet. (Not a problem though!).
dd2 is 22 and still (severely) lactose intolerant. label reading is a way of ife but she takes a pill from the Health shop called Lactase when she wants to occasionally indulge in something creamy but is frightened of taking it too often in case she becomes immune to it.