Aging and your epigenome
Some researchers used to think that aging occurs because DNA in the cell degrades over time. But the cloning of cells (and animals) has now decisively proven otherwise.
For cloning, scientists take DNA from older animals but the cloned sheep are never born with signs of aging and are always normal healthy babies. If aging occured primarily due to DNA mutations, then cloned sheep (or cells) would be born old.
This means that the primary reason lies somewhere else, and Dr David Sinclair, one of Australia's most distinguished researchers, believes that we have finally found its root cause.
According to him, the emerging consensus is that aging occurs due to loss of information in the epigenome, not the genome (or DNA)
Since all cells in the body has the same DNA (genome), how is it that some cells become hair cells, other skin cells and so on and so forth? Obviously, something other than DNA must be influencing which genes express themselves in which part.
This "something", in very crude terms, is called your "epigenome".
With age, your epigenome degrades. That's why, for example, hair starts appearing in places where it's not supposed to, because the epigenetic information that tells cells to assume a particular identity, is distorted.
The good news is that this epigenome can be restored to a high degree, and has successfully been done, in many animals. This means that aging, in theory, cannot just be stopped; it can effectively be reversed.
Currently, several human trials are going on for various drugs that have shown remarkable promise in early stages.
(Summarised from "Lifespan - Why we age and why we don't have to". The exact single cause of aging that Dr Sinclair explains in the book is beautiful, but far too complicated to fit in this post)