Average refers to the average age of death of all humans born that year on planet earth. The current average lifespan is ~72 worldwide and ~85 in Japan (highest national average).
You express the object of the bet as "average age of death of all humans born that year on planet earth.", which I interpret literally as waiting until all people born in a certain year die and measuring their actual average lifespan.
But after stating that definition, you quote as example life expectancy values, and link a life expectancy graph. Life expectancy is defined as the expected age simulating a person being born now with age-specific mortality rates frozen at their current values throughout their life.
Which one is the actual object of the bet?
@rotatingpaguro The actual object of the bet is your original interpretation. Granted, reported life expectancy is different. The link I quote was intended to be informative even if not directly answering addressing question.