Longevity Pedigree

I first read about this Longevity Pedigree chart idea from the organizeyourfamilyhistory.com blog.  According to the blogs owner, Janine Adams, you sketch a pedigree chart with just your ancestors name, age at death, and some even included cause of death.

This is my Longevity Pedigree chart.

What I can see is I have a lot of question marks. But what I also see is the average life span of my family is the age of 70 (20 names with death ages added together equals 1396).  Most likely filling in the question marks with more death ages will up that average death age of 70.   I need to do this.