This open access paper contains an interesting discussion of genetic investigations in the oldest of people who manage to avoid age-related disease and stay comparatively healthy: "Individuals who live to 85 and beyond without developing major age-related diseases may achieve this, in part, by lacking disease susceptibility factors, or by possessing resistance factors that enhance their ability to avoid disease and prolong lifespan. ... Besides genes that have been shown to affect lifespan in animal models, a limited number of genetic variants have been reported to be associated with long life in humans. These studies mainly evaluated genetic variation linked to extreme human life spans (e.g. centenarians) without focusing specifically on health. ... Controversy exists regarding the contribution of these and other gene variants to aging and longevity, because replication studies in different populations, as for replication studies in complex diseases, more often than not fail to confirm the initially reported associations. ... Healthy aging is a complex phenotype likely to be affected by both genetic and environmental factors. We sequenced 24 candidate healthy aging genes in DNA samples from 47 healthy individuals aged eighty-five years or older (the 'oldest-old'), to characterize genetic variation that is present in this exceptional group. These healthy seniors were never diagnosed with cancer, cardiovascular disease, pulmonary disease, diabetes, or Alzheimer disease."

Link: http://dx.doi.org/10.1371/journal.pone.0006641