I'm 52, and was told in 2008 that I had the "DD." And I did not start out PI. At all.
Prior to this my mutation was always "unknown" and that could be from going to different clinics, I don't know.
What I do know it that I was diagnosed at 5 only because my brother was born with a severe case, and once they finally figured out what was wrong with him, we were all tested, even my parents. This was 1964.
I would be tested 3 more times in my life, different years, because I showed NO symptoms, and each set of doctors thought the others had made a mistake. They finally decided I had a "mild" case. And I did. There were years there that I didn't even bother with going to clinic.
In 2008, that changed. I went into the hospital for the first time in 20+ years (the first time was because of an over-active doctor) that August. It was as if I'd been diagnosed for the very first time. This thing that had lain dormate in me for years surfaced with a venegance. BUT I came home, got serious about loads of greens, carrot juice, cases of water and my 3 day a week workout. Fortunately, I was able to cut back on my career in the advertising field. And I'm doing fine!
The point is, I did not start taking enzymes until in my 40s, occasionally. Now I take them alot, but still not for every meal. So in my humble opinion, it can and does occur more gradually. Remember, they still don't know what they think they know about CF and the mutations. I'm still proving them wrong... and you might too. So take heart, eat GOOD healthy food, and know that every body is different, no matter what the "experts" may say.