Assessing centenarians at age 80 is more informative than at age 100 due to high mortality at 100.

“i don't care how they look when they're 100 years old because now 30 of them will die next year so no matter what i measure it will either be the predictive of their death next year or they're predictive of their longevity before right the better thing is when they were 80 how do they look compared to their 80 year old non-centenarian peers”