I agree too with HollyCatheryn, but also totally with Emily. I was diagnosed when I was 11 so just coming up to my teenage years and I really think it is the worst time. Everything is changing anyway at that age, so having this to deal with as well is very hard. All you want at that age is to be accepted, but then this thing comes along to make you different to everyone else. Obviously, I have no comparison as to whether it really is the most difficult age, but I believe it anyway!
I do also think (in answer to the original question) that as much as there is always a new issue to deal with alongside your cf (or because of it) as you reach adulthood, the whole idea of cf, the fact that you have it, is easier to deal with and accept. I think this is maybe because it is easier to be open with people about it (in my case anyway) as children can be harsh, but adults are more understanding in most cases and so do not judge you badly for having a condition that is obviously out of your control anyway. You learn how best to deal with all the treatments, how far you can push your body etc and also you chill out more about things like having to join in every single thing like going out when all your friends are etc, so you can more easily choose to stay home one night to do your meds instead without feeling you are missing out on life so much.
I really think that being diagnosed at such an odd age meant I didn't fully appreciate the severity of the condition and the things I could do to help myself, to keep myself well and to prevent myself becoming sicker. I really skipped a lot of treatments and when I look back I wonder why, as I often felt ill and the way to stop that is by doing the meds. but that kind of knowledge only comes with age, wisdom and acceptance and I was at the totally wrong age to accept what was wrong with me. As child, living with it your whole life, you know no different and just go with it, and as an adult, you are generally more accepting of life and all that it throws at you. Also, like hollycatheryn said, I now have things that I really want to live for. I am getting married this year, and do all of the things I am supposed to as there is no way I intend to leave early and miss out on all the wonderful things I could experience with my husband to be. As much as I had a loving and supportive family growing up, it's not the same as having someone who loves you and who you love back, willing you on and wanting to be there with them for as long as possible.
Sorry, I totally went off the subject.
That's only my viewpoint, but there it is.