Plausible, Robust Old Age
The plausibility of good lifestyle choices leading you into a robust old age - judged by the medical technology and possibilities of today - makes a big difference when looking at the future. The length of your healthy life in the long term is far more dependent on future anti-aging medicine than anything else - how effective it is, how fast it is developed, how much you supported research - but reaching the era of working anti-aging medicine while still being healthy enough to benefit is a matter of working with what you have now, using the health tools of today. Here, the Deseret News notes a study that suggests reaching your mid-80s in good health, using the technology of the past 50 years, is perfect plausible for most people. You can do the math based on your age and the predictions of futurists to see where this might get you.
Link: http://deseretnews.com/dn/view/0,1249,635172165,00.html