There is only one medical research study on the lifespan of individuals with Pectus Excavatum (PE). For those interested, it can be found here. In that study, it was determined that out of 50,946 autopsy reports included in the research, there were 62 cases of PE. As a whole, PE individuals tended to die at a younger age. However, PE individuals that lived past 56 actually had an increased lifespan.
It is very important to realize that in this study, PE individuals included many diseases such as Marfans. In general, patients may have PE and other co-existing diseases, or some may just have PE alone. This study did not specifically focus on patients with PE but without other diseases.
All in all, there is a significant lack of research on this topic and it is not clear what the exact effect of PE is on lifespan.