I'd just like to say that type 2 has been traditionally associated with older people, but I think Rachel probably has type 1 which has traditionally been called juvenile diabetes (although you are right that t2 is beginning to reach younger people). Eating habits have nothing to do with someone being t1 - it is an auto-immune disease (and t2 sometimes has something to do with diet but I think it's a lot to do with genetics) but of course your diet has to change once you become diabetic as carbs and insulin are so hand-in-hand with eachother. When you have to take insulin you need to be careful of the activity you do until you understand how it affects you as this can lead to hypos, so I woulnd't recommend a huge amount of heavy exercise unless someone knows what they need to do to keep sugars at a good level during and after. I'm speaking from experience here as I'm type1 and have been for 14 years.
Rachel, a lot of this is trial and error - you find what food affects you more than others, and by no means stop exercising! It just means you have to be a little more careful than most, and as tiadesai rightly says doctors etc will really help you out if you find someone who specialises in diabetes.