A lot of CFers get told they have asthma or this that and the other thing for good portions of their lives. There are several people on this site that didn't get diagnosed until they were adults. It is a major thing, and definitely important to know, but quite frankly... doctors that don't specialize in it, generally wouldn't know CF if it smacked them in the face. It seems surprising to us, but there's a lot of ignorance out there about it.
As for what to expect... you can't, really. Meds and therapies are changing all the time, life expectancies too. Plus every CF case is so incredibly different. Some people die before they hit 20, others on here are in their 40s and 50s. If you're curious about the things that could *possibly* happen, I say browse the site. There's a whole lot of stuff we could address, and it'd take forever. Besides, if you browse, you can look at stuff you specifically want to know, things that are particularly important to you instead of *everything* all at once.
If you have any more questions more on the specific side (as opposed to "what should I expect?"), those will be more easily answered right in this thread. Otherwise, definitely look around. There's all sorts of threads about all sorts of aspects of CF.