[Jagdgewehr]

The control group does not have retirees from other industries. All the retirees in this study are from Boeing Aerospace.
The conclusion should say "For every year worked beyond age 55, Boeing Aerospace retirees lose two years of life span."

[HiTech RedNeck]

Might it be that the people who can retire early have more money (possibly from other sources than the job) and thus can afford a less stressful lifestyle and better medical care.