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.