Ageing (a probabilistic decline in a cells ability to repair itself) is a complex process. It is very likely that the aging process is driven by the interplay of different cellular mechanisms, in feedback loops both, exo and endogenous, resulting in damage to a cells to ability to self-repair.
Whilst that complexity and the involvement of DNA damage and epigenetic modifications are no doubt linked it is also the case that chromatin defects ( the cellular structure packaging the combination of DNA and proteins ) plays a key role in ageing.
A key research question is how these processes are linked. Is it that DNA damage leads to chromatin defects? Alternatively, that changes in chromatic structures impacts DNA replication. Most recently it is hypothesized that DNA damage, epigenetic processes and chromatin aberration are more of network of interlinked processes and that a straight linear explanation may be too simplistic.