Every year you are alive increases your life expectancy. Infant mortality is factored into that 76 years, so are other unnatural causes of death. If you actually live a "normal" life and die of natural causes, 40-45 feels more accurate to me as "middle aged". Even though 76 is the average, I believe 86 is the peak (mode/most common) age of death. If you think about it that makes sense. 99% of people die before their 92 birthday, so there are only 6 years to fit on that side of the peak but 86 years (far more opportunities to die of unnatural causes) on the other. This is why averages are very misleading. Even though 76 is the average, it's not when the largest amount of people die.