I'm fifty. I'm not the same guy I was when I was forty, or thirty, never mind twenty, or ten. I visualize identity not as a solid object but as a wave form travelling along the temporal dimension through a complex emulsion of memories, experiences, and emotions, bounded at front and back by singularities—boundaries beyond which there is no continuity (and almost certainly no persistence of identity). We're all waves travelling through this common soup of human existential phenomena, occasionally refracting through one another and being changed thereby. And as we move, we change. Not only are our physical bodies not made up from the same individual atoms: the bits you could notionally use to describe us change, too. New data is added, old patterns are lost (I have the memory of a goldfish these days).
Beyond the obvious (gross physiological deterioration and pathologies of senescence), what are the psychological symptoms of ageing?
I tend to be somewhat impatient or short-tempered these days. Examples: getting worked up about people obstructing a sidewalk in front of me, or carelessly blowing smoke over their shoulder and into my face, walking while texting ... you know the drill. This I put down largely to the chronic low-grade pain of the middle-aged body: joints that creak and pop, muscles that need an extra stretch, sore feet. Certainly dosing up on an anti-inflammatory like naproxen or diclofenac is mildly helpful: if it wasn't also associated with a slightly elevated risk of sudden cardiac death I'd do it all the time. (I take special pains to be mindful of this tendency when driving, and compensate accordingly: wearing a couple of tons of metal and travelling an order of magnitude faster than on foot raises the potential costs of impatience from trivial to lethal. But then, I probably spend less than a hundred hours driving in any given year. Driving isn't routine any more (although I used to commute around 20,000 miles/year for work, back in the dark ages of the 1980s) so I can usually keep track of it.)
My memory, as previously noted, is a sieve. Partly I find myself living in a cluttered cognitive realm: I have so much context to apply to any new piece of incoming data. If middle-aged people seem slow at times it may not be because they're stupid (although stupidity is a non-ageist affliction) but because they're processing a lot more data than a young mind has on hand to digest. That shop window display? You're not just looking at this seasons clothing fashions, but integrating changes in fashion across multiple decades and recognizing when this stuff was last new. (And if fashion is your thing, you're trying to remember how far back in the wardrobe you hung it last time you wore it, all those years ago.) A side-effect of this: when experiencing something familiar through long repetition you forget it — you don't remember it as a new experience but merely as an instance of a familiar one and (eventually) as nothing at all. (For those of you with a workday routine, this can cut in quite early: how well do you remember your last commute to work? If you do remember it, do you remember it only because it was exceptional—a truck nearly t-boning you, for example?)
An intersecting effect of the aches and pains and the difficulty retrieving information is that you have to focus hard on tasks—it's hard to execute a day with six or seven distinct non-routine activities in it, because that requires planning and planning requires lots of that difficult mental integration. Planning is exhausting. Instead you focus on maintaining routines (get up, brush teeth, take meds, shave, use toilet, make coffee ... check. Go to gym: check. Eat lunch: check. Work at desk: check ...) and scheduling one or two exceptional tasks. Mental checklists help a lot, but you run into the sieve-shaped memory problem again: this is where digital prosthesis (or an overflowing filofax) come in handy.
Your perspective on current events changes. Take the news media. Everything new is old after a time: you see the large-scale similarities across decades even without becoming a student of history. Today's invasion or oil crisis is just like the one before last. Our current political leadership are stuck in the same ideological monkey's-paw trap as their predecessors the last time their party was in power. And so on. So you tend to discount current events and lose interest in the news until something new happens. (If you're wondering why I'm obsessively interested in the Scottish independence thing this year, it's because it's a disruptive event: nothing like it has happened in UK politics for a very long time indeed. It's fresh.)
The same thing happens to one's interest in the current celebrity culture or pop stars. I haven't heard any of Taylor Swift's music. Or Amy Winehouse's. I have no idea about the Kardashians other than that they're famous for being famous. These people are successful players with careers that follow a handful of standard trajectories: well, good luck to them with it. If they make music that speaks to me I'll hear some of it sooner or later and then start exploring their back catalog, but I feel no urge to get sucked in by the hype and excitement right now. Been there, seen it all before. (The last live concert I went to was Nine Inch Nails; the next will probably be Lene Lovich. That should tell you just how non-current I am ...)
Planning takes on a different perspective because your relationship with time frames alters. When you're in your early 20s retirement seems infinitely far away, and the idea of laying plans for a 25 year span is positively surreal. But when you're 50 you've experienced multiple such overlapping periods. You can recognize gross patterns and trends in your life and understand how to set your sights on goals years in the future. My work, these days, often involves planning and executing projects that take months to carry out and must be scheduled years in advance. As an extreme example, I'm midway through a personal project (performing some rather informal A/B testing on two ongoing series of books) that will take 3-5 years to get any useful information out of. So, while short-term task-juggling becomes harder, really long-term project planning gets paradoxically easier.
Interpersonal relationships change in scope, too. Everything is intense and fresh and immediate when you're young. Emotional engagement is high. Emotional engagement doesn't necessarily slacken with age, but the amount of energy we can bring to bear on our relationships diminishes along with our stamina. Watch a pair of 70-80 year olds who've been together for half a century some time. They often appear to ignore each other, because they have such a strong internal model of the other's mind that they can anticipate their partner's words or actions: it's an ignorance derived from deep insight and familiarity, not obliviousness. There's some evidence from cognitive psychology that we use our partners or children or other relatives as external content-addressable memory storage, relying on their shared experience to fill in our patchy recollections: just like google. (Google isn't making our memory obsolete, rather it's plugging into an existing interpersonal human mechanism at a very low level.) At the same time, they may not notice or be able to respond effectively if their partner is undergoing an exceptional crisis such as a stroke or heart attack: the phenomenon is so far out of scope that they don't recognize it as an emergency at first, unless their attention is specifically redirected from their mental map of the other and back to the human territory it represents. Especially as our stamina diminishes with age, until in extreme old age even focusing on our own immediate needs is a challenge.
So, you've been reading a Charlie Stross blog entry and you're wondering where the zinger is.
Here's the speculation. Let us suppose that in the next couple of decades we develop a cure for the worst problems associated with senescence. We figure out how to reverse the cumulative damage to mitochondrial DNA, to reset the telomere end caps of stem cells without issuing carte blanche to every hopeful cancer in our bodies, to unravel the cumulative damage of prion proteins, to tame the cumulative inflammation that causes atherosclerosis, to fix the underlying mechanism behind metabolic syndrome (the cause of hypertension and type II diabetes).
We now have a generation of 70 year olds who in 20 years time will be physiologically in their 40s, not their 90s. At worst, they're no longer in the steep decline of late old age: at best, they're ageing backwards to their first flush of adult fitness.
You're one of them. You're 25-60 years old now. You're going to be 55-90 years old by then. Unlike today's senior citizens, you don't ache whenever you get out of bed, you're physically fit, you don't have cancer or heart disease or diabetes or Alzheimer's, you aren't deaf or blind or suffering from anosmia or peripheral neuropathy or other sensory impairments, and you're physically able to enjoy your sex life. Big win all round.
But your cognitive functioning is burdened by decades of memories to integrate, canalized by prior experiences, dominated by the complexity of long-term planning at the expense of real-time responsiveness. Every time you look around you are struck by intricate, esoteric cross-references to that which has gone before. Every politician, celebrity, actor, blogger, pop star, author ... you've seen someone like them previously, you know what they're going to say before they open their mouth. Every new policy or strategy has failure modes you recognize: "that won't work" is your usual response to change, not because you're a curmudgeonly pessimist but because you've been there before.
Maybe you're going to make extensive use of lifeloggers or external prosthetic memory assistance devices—think of your own personal google, refreshing your memory whenever you ask the right question—or maybe you're going to float forward in time through a haze of forgetting, deliberately shedding old context to make room for fresh. Some folks try for rolling amnesia with a 40-70 year horizon behind them. You gradually lose contact with such people because they just don't want to know you any more. Others try to hang on to every experience, wallowing in the lush, intricate texture of an extended lifespan until their ability to respond is so impaired that they appear catatonic.
Which are you going to be? And how will you cope with a century of memories contained in the undecaying flesh of indefinitely protracted adulthood?