Well, in my case, it's a slow descent into death, and I am already past my expiration date.

Yes, it’s called senility.

You mean like on dairy products?

Not clear on the exact question you're asking.

I've been a knowledge worker my whole adult life (software development) and am now 61. So far, I'd say past age 50 or so, certain aspects of mental acuity have slowed down. It pretty much mirrors my physical deterioration. I go up and down stairs far more slowly, walk far more carefully on uneven sidewalks and the like. My balance and proprioception always were sub-par anyway, and now I can't rely on quick reflexes to save me from spills. It's like that with my mind -- I can still function so long as I'm methodical and careful in certain contexts. I take better notes, make more to-do lists that I used to keep in my head, etc.

But this is highly individual. And it's also somewhat a function of the work you do. My work requires intense focus and the holding of large abstractions in your short term memory. If I didn't need to exercise those faculties I probably wouldn't notice any issues. As it is, my main problem is probably with juggling distractions. Sometimes I have 3 different people at work trying to interact with me, my wife wants something, the dog needs walking, and I just give up in frustration and end the day early as I know I'm not going to do anything but thrash around from that point on. Fortunately I'm in a position to have that kind of flexibility. The billable hours take a bit of a hit though.

My wife is forgetting a lot of things and worries about early onset dementia. In her case I think it's just the effects of lifelong insomnia and anxiety, which, even though she is making real strides with that, has probably fried a few circuits by now. So it's unclear how much that will improve with better sleep, and how much is permanent damage. I have a physical version of that, had chronic Lyme disease for many years and although cured now for the past 15 years or so, have residual joint damage from it. Also Lyme may have effected my brain.

So many factors in the mix, and so many individual strengths and weaknesses, that you really can't make generalizations. Nor is there much point; our next door neighbor just got a stage 4 pancreatic cancer diagnosis, so mental acuity is the least of her concerns now. Anything can turn to shit at this point in my life, for any reason or for no reason, so I don't worry too much about trying to control it. If I did, I'd be awake at least as much as my wife, and then things would just break sooner.

Please define expiration date. Is it when the brain cease functioning or the mind not controlling you
Tough one

Sure, but everyone has a different limit. I've seen my grandmother and aunt die with alsheimers, my grandfather die with emphasima, my brother die from a heart attack, and my father (sharp as a tac) die because he was ready. We all stop ticking sometime.

Definitely does have an expiry date, unless somethign else kills you forst, the baain dies like all cells. My memoey is not as fast as it was, for now my capacity for leanr new things is still strong, but I probably will forget them soon.

It's probably the same date asthe expirydste on your birth certificate! Lol..

Yes.

Our capacity for thinking does not fade - it simply takes longer to process thoughts - and becomes harder to remember our conclusions.
When I was 20 I thought faster than my mouth could handle. Now I'm 76 I have to time-share resources between thinking and mouthing my thoughts - and if I allocate too much mouth time, I forget the next part of the thought! The same , of course, applies to writing them down.
I know I had a good idea - I just can't remember what it was!

I don't think so... I've met some very old people sharp as a tack

I turned 55 today and I'm prone to go with the slow death of my intelligence. I know I have it, I just don't remember where I left it.