Out of the many fears of aging, I have one I seldom see mentioned: fear of moral deterioration. You can find a thousand discussions of our coming physical disintegration, and how our short-term memories will begin to fail, but the thought seems to be if we can fix those, everything's gonna be pretty good. Live to 120 - go for it. That we might become in some way worse people doesn't enter into it.
I spoke with a young woman today who had been given a bracelet by a mentally ill person. The bracelet turns out to be worth $21K. Her husband wants it back. Yesterday, the young woman told me that she had brought it to a pawn shop, found out it was valuable, and given it to someone to sell. Today there was a subtle change in her story. She had given the bracelet to someone and then found out from him it was valuable, so he won't give it back. An enormous difference, and clearly a story she is telling herself to self-justify. I thought immediately of Gollum's story about his "birthday present." That lie was wrapped around a bit of truth, changed over the years. Most lies are.
There is also the chapter in The Screwtape Letters in which Wormwood is told not to panic at his patient's religious conversion, as there are many long, quiet years in which to slowly steer him toward Hell. It is hardly surprising to see a theological similarity between Lewis and Tolkien, but I think this is echoed in great literature over the centuries, at least in the Western tradition. We change our stories over time, fitting them into the narrative we prefer. It is not that we can never absorb uncomfortable information about ourselves and integrate it into our understanding of the world, but we resist it. We cannot be counted on to own up to our shortcomings. We will admit some, but others we will slowly change, enlarging our own virtue and innocent victimhood.
I don't suppose there's much in the way of evidence that this gets worse as we go along, but I have to think it is cumulative most of the time. We may do most of the reworking in the first few months or years, and living another decade or two may not add to the lies much. Some lies we may be able to reverse a bit because of added wisdom. My worry is that these are very much the exception. I consider what stories I have already changed and no longer even acknowledge that to myself. Perhaps I was better person 10 or 20 years ago. I haven't noticed any improvement in self-honesty - I hope there has been no worsening. Yet even if the worsening is slight, what does that mean for humans living to be 100, 140, 200 years old? We may become horrible to behold.