If "A Wizard of Earthsea" is a boy's coming-of-age and "The Tombs of Atuan" is a girl's coming-of-age, then "The Farthest Shore" is a mature reflection on power, its limits and the deeper purposes of life.
The storyline concerns the disintegration of magic - a side effect of a maverick sorcerer, Cob, who develops a great spell to ensure his own immortality. Le Guin portrays this as the ultimate destabiliser of the balance of life, the harmony of all existence. Death-removed is stasis; death is the prerequisite for the renewal of life.
Very Taoist and emotionally satisfying, even a little convincing; but my inner skeptic has qualms.
The modern theory of aging is that of senescence although controversies rage. But as Greg Cochran observes, in theory it should be fixable. In surveys, people seem to be split as to whether they would take up an offer of personal immortality.
If I was offered a course of treatment which rendered me immortal, I wouldn't be interested. I'm too stupid and slow at age 66: I see only voyeuristic tedium in millennia to come. But perhaps the salesman has an upgraded deal?
Perhaps my ageing, error-strewn DNA could be debugged and re-implanted somehow to make a quasi-clone. A new, vibrant baby-me, ready to start a new life without all those burdensome memories and bodily breakdowns. When I was such an infant, I'm sure that I was up for life .. so that would have to be a yes, then.
But why stop at cloning? Why not introduce some extra variety, explore new regions of the corporeal and psychological state-space? Sounds like an even better plan.
Oh, wait. You say we do that already?
I think it's an open question as to whether a society which had genetically-engineered extremely-long life would have strategically greater reproductive success than current-lifespan societies. That is the issue at stake here.
One day some society will try it - and evolution will have another sub-species to test..