An interesting open access paper via PubMed Central: "Strictly speaking, 'epigenetics' refers to chromatin and DNA modifications that are heritable through cell division, but do not involve changes in the underlying DNA sequence ... Chromatin structure is not fixed. Instead, chromatin is dynamic and is subject to extensive developmental and age-associated remodeling. In some cases, this remodeling appears to counter the aging and age-associated diseases, such as cancer, and extend organismal lifespan. However, stochastic non-deterministic changes in chromatin structure might, over time, also contribute to the break down of nuclear, cell and tissue function, and consequently aging and age-associated diseases. ... it is apparent that chromatin structure does change with aging, in organisms as diverse as yeast and mammals. However, with the exception of Sir2 in yeast, the extent to which this impacts the aging process has not yet been defined. ... the effects of chromatin on aging are likely to be complex and bidirectional. To test and define the impact of specific epigenetic determinants on aging will be a challenging task."