Ok so the long and the short of it is, yes you can develop an intolerance, if you are an adult and 'develop' it, then it could be that you always had it and until now hasnt been a problem, or you are just more senstiive to it now due to other factors. And not it isnt always genetic, ie. not always passed on from a parent. It can be tested for and singled out on  your own unique DNA chain, but often times it can be a number of environmental factors contributing to the problem.

It is also worth mentioning that there are a few things that can be inferred by the word 'intolerance'. Like, is it anything containing lactose, dairy in general, or if it is cooked/prepared a certain way. IE. A friend of mince cannot eat the pre-packaged grated cheese from the supermarket due to being intolerant to the preserving agent they use so the cheese doesnt go hard at the edges.

It may also be a sign of bigger problems. Like do you get cramps, bloating, wind, diarhhoea or stomach upset when you eat dairy? What about other foods high in fat or oily foods? This may be a sign you have irritable bowel syndrome or something of that nature. My DP used to have an iron stomach, and now struggles with some foods he would never have looked twice at.

Best of luck with your query, and hope I have been of some help and not confused you too much!

Up to you, really - an intolerance is very different from an allergy, and an allergy shouldn't ever be left out of a family medical history.  When I was going over that stuff with my midwife, I told her about some of my mum's health issues, but also added that she's hyper-attentive to any changes in her health and always chooses the longest most medical name for every ailment.  In other words, I've included some stuff that I am dubious about whether or not it's a serious issue, but with a disclaimer! 

When I was 13, I was diagnosed with Asthma (incidentally it was the same year that we moved to NZ!) I learnt over the following few years that certain diary products trigger an attack or made me wheeze. I tend to tell people that I have I am lactose intolerant / diary intolerant - as its easier than saying: I can eat cheese, but not milk / cream / ice cream / yoghurt etc.  Although I am fairly careful - I will very occasionally have an icecream, but only if I am "well" and I will always monitor myself afterwards.