On my last check up my PFT's were in the high 90's. One part was like 112% (though I forget which). But my bigs, and more importantly my small airways were very high. I am 37 years old with two mutations. I weigh 200 lbs and stand 5'11.
Given those stats, and how I only have "very slight" bronchiactasis at my age you would think I have very mild CF. Not the case. Mild compared to many others on here, but from the crap I went through in the past, not mild. The PFT tech who gives me my tests everytime told me that "If it wasn't for your diagnosis, these readings would not show you had CF. These look like healthy lungs". I then asked him how his readings were (because I know he just had to test himself out of curiosity). His readings were in the low 60's. He told me he smoked a ton when younger, and now his lungs kind of suck.
The point of all this is, regardless of disease or no disease, there are tons of variables that come into play when comparing a "normal" person without CF, and a very well taken care of person WITH CF. I've had explosive, life threatening lung bleeds, many infections, double pneumonia, on deaths door, I culture two different fairly resistant lung bugs (staph and PA) with other flora present (seratia, yeast, etc) etc...And I'm still here with very high PFT's, and thriving quite well.
You can have someone like myself with odd variables (mutations, strict compliance, etc etc), that has healthier lungs than non CF patients who actually give the tests. To be honest, variables aside, ask your PFT tech about the "predicted" numbers. They basically use your age, height, weight, and gender to show what you SHOULD be showing if you were "normal".
These numbers are not a real weathervein to determine how you really are though. I have known some people with very low PFT #'s that felt, and acted much better than me. I have also known CF's with much higher PFT's than myself that felt like crap. PFT's aren't the end all be all of definition of your health. It's a fairly good general ruler yes, but people act either positively or negatively depending on how they FEEL.
Remember not long ago when an article was posted about various PFT test levels and bronchiactasis? A couple people in that study had very high PFT scores, but were riddled with bad levels of bronchiactasis. Our health level is a large average of many different factors. Don't let one factor rule your universe.