A couple of things here...
There is some evidence that suggests that your gene class combination may aide in predicting clinical outcome. However gene class doesn't take into account phenotype which is equally important when discussing genes. It also doesn't take into account compliance, environment, bacteria cultured, nutrition, exercise, luck, etc. There is plenty of evidence out there regarding siblings and even twins with the same genes that have completely different clinical outcomes.
One other note on genes is that DF508 is the most common, not the most severe. DF508 is a Class II gene usually associated with defective trafficking of CFTR so that it does not reach the apical surface membrane where it is intended to function.
Also, the median age is 36ish which isn't exactly the same as life expectancy. Here's some info from the CFF...
<div class="FTQUOTE"><begin quote>Using data from the CF Foundation Patient Registry, which is gathered from patients treated at CF Foundation-accredited care centers, we do know that more than 40 percent of all people with CF in this country are 18 years or older. In addition, we have calculated the predicted median age of survival. This number is based on a statistical method of using life table analyses developed by insurance companies to calculate trends in survival.
In 2005, the predicted median age of survival rose to 36.5 years, up from 32 in 2000. The predicted median age of survival is the age by which half of the current CF Patient Registry population would be expected to survive, given the ages of the patients in the registry and the distribution of deaths in 2005.</end quote></div>
A lot of new parents/new DX want to try and get their heads around what the future might mean for their CFer but the fact is no one can really tell you that. All you can do is provide the best care possible and pray.