Life expectancy at birth is one of the single best indicators of societal well-being. So many things have to work well for the great majority of people to live long lives that the high life expectancy serves as proxy for holistic well-being. The measure is of particular value in that it measures something relatively concrete, as opposed to income (which has varying impacts relative to local living standards and exchange rates) or happiness (a highly subjective term.)
Throughout human history, global life expectancy at birth was about 30 years. This does not mean that everyone died before age thirty. It is an average age of death. One in four children died before their first birthday (it is less than 1% in developed nations today). Some people lived to be quite old. But on average people lived to be thirty.
Over the past two hundred years, something has changed. Global life expectancy at birth has more than doubled and it is still improving. I won't give a dissertation on why that might be but rather invite you to realize that contrary to our intuitions, news reports, and personal biases, we are living through the most astonishing improvement in human flourishing in human history.
Here is a chart showing the trend.
This chart offers an animated presentation of the improvement by nation.