Wired has some anecdotes from people trying Resveratrol and other attempts to extend life. The reasoning is that Resveratrol and calorie restriction should not be harmful and might extend life. People want to live long enough and be healthy enough to take advantage of truly effective life extension methods. Perhaps methods from SENS
The other aspect is that people can track their actual health markers and how they feel. Aging markers like body composition, physical performance, bone mineral density, peak aerobic capacity, Cholesterol levels, and plasma glucose and insulin levels.
Here is a site that list aging biomarkers and possible treatments