When looking at most of the past extension of human life since the 1700s the major causes were better sanitation and control of infectious disease, with the largest effects on life expectancy at birth arising from lowered childhood mortality, even though there was also a steady increase in adult life expectancy. When looking back at the late 20th and early 21st century period from a safe distance of a century or so, the similar high level summary of the drivers of life extension will probably focus on greatly increased control over cardiovascular disease and the resulting steep decline in late life mortality due to this cause. There are many other improvements in medicine that have occurred in the past fifty years, but this is the one that stands out if you look at the data.
This period of medical strategy and development is coming to an end, however, and the summary of the next age in medicine with regard to its effects on human longevity will be that this was the time in which researchers started to directly address the processes of aging and, separately, brought cancer largely under medical control. Progress in the future of life expectancy at this point in time is overwhelmingly a matter of success in intervening in the aging process, building biotechnologies to repair the cellular and molecular damage that causes aging and thus prevent or turn back age-related frailty and disease.
If aging is purely a matter of damage we should expect all improvements in long term health to also extend life to some degree. If there is less damage then the machinery lasts longer - it really is that simple a concept, even though the machinery of our biology is very complex. Studies of changing life expectancy such as the one quoted below continue to find that aging appears to be plastic, and that present trends in reduced old age mortality are continuing in those regions with better access to medical technology. The only limits on life are imposed by a present inability to fix the problems that kill us, and that can be changed by funding the right research:
In high-income countries, life expectancy at age 60 years has increased in recent decades. Falling tobacco use (for men only) and cardiovascular disease mortality (for both men and women) are the main factors contributing to this rise. In high-income countries, avoidable male mortality has fallen since 1980 because of decreases in avoidable cardiovascular deaths. For men in Latin America, the Caribbean, Europe, and central Asia, and for women in all regions, avoidable mortality has changed little or increased since 1980. As yet, no evidence exists that the rate of improvement in older age mortality (60 years and older) is slowing down or that older age deaths are being compressed into a narrow age band as they approach a hypothesised upper limit to longevity.