"Would you rather live in the ascendancy of a civilization or during its decline?"
–Arnold Poindexter, Lambda Lambda Lambda, Revenge of the Nerds, (1984)
This question has always bothered me. What possible benefits could there be to living in a civilization in decline? Or was it just a sign that he was wasted on Booger’s Wonder-Joints?
How would I know if what I’m experiencing is the ascendancy of a civilization if my lifespan is only a few decades?
Presumably, in it’s decline a society still has the remnants of what it achieved: art, culture, technology, infrastructure etc. Things are slipping- upkeep, resources, social fabric etc, but the heights achieved still impact society.
How close to the apex and how fast are the decline and ascendancy?
You couldn’t. The question assumes a viewpoint from the future looking back, like we look at the Roman, Byzantine, or the Mayan civilizations.
I don’t believe that was specified. Are you suggesting that it would be better to live during a gentle decline than a rapid (presumably chaotic) ascension?
I’m saying I’d like to live as close to the apex for as long as possible.
Obviously. But assuming that each alternative was equally close to the apex, and you must choose one, would you pick the ascendancy or the decline?
Then I don’t care either way. Why would I?
In one scenario things get a little better every day; in the other, things are continually getting worse. You don’t see a difference?
In the former they started out worse. You just said that on average they’re equally good. Hell, if anything I’d take the one in decline because then the best days would align with my youth.
But in an ascending civilization you would presumably have better and better medicine and health care as you got older instead of memories of things like artificial hips and cancer treatments.
A mini example.
The early days of space exploration, the space race, the lunar landings, Skylab, Apollo-Soyuz, and the early days of the space shuttle. Things were exciting, anything was possible and things were just getting more amazing and better.
The latter days of manned space exploration. This shit is hard, we can’t even do what we USED to be able do. What we are doing is a pale comparision and seems to have no point because at this rate we will barely doing anything at all and finally won’t be doing it at all period.
The early days were inspirational. The latter days have almost been soul sucking.
I’ll take the rise over the fall any day, even if technically the absolute “level” of the fall is higher than the “level” of the rise, assuming you kinda know where you are in relation to the peak.
Is “the middle age” an option? That, if so, otherwise early decline.
The entire healthcare system is going to collapse in the span of a couple decades?
You think that’s unrealistic?
If you posit that the decline happens at the same rate as the climb? Yes.
Decline, obviously. If you buy the maunderings of an earlier generation of moralistic historians that linked political decline to moral decline*, then obviously the best time to be alive is when everything is sinking into wretched wallow of hedonism and excess. Because who doesn’t love hedonism and excess? 
Seventy years ago life expectancy (USA) was 63. Today it’s 78. Now imagine that same rate in reverse.
Some to participate, others to excoriate.