COPD at 28 years old.

I have suffered recurrent chest infections, pneumonia and wheezing for years. I recently had a Spirometry test which indicates COPD. They've arranged for another test in 2 weeks and

I was a heavy smoker for 8 years but quit 5 years ago. I have a 3 year old and 18 month old. When well I am very fit and active. As a family we are always in the country. I can walk 10+ miles over mountains with my youngest on my back. Most days we walk the dog 3-4 miles at least once. I am just devastated. How is it possible to have COPD when I am as fit as I am? What does this mean? I am usually a level headed person but I am in a blind panic. I work for the ambulance service so know the implications but my sister says I just see the worst case scenarios which is likely true. I am so scared of dying young. If I have it at 28 what will I be like by 50? Will I even live to 50?

Sorry for the pity party. Just very confused right now.