Our bodies need to perform different roles as we age and mature. We'd also need different sets of skills depending on our current developmental phase. It would make sense for our brains to change too, that the developmental path of our brain is planned to make it undergo changes that'd make it more adapted to the tasks it'll have to tackle over different developmental phases.
It'd make sense for our brain to be more fine tuned for grabbing resources from family when we're a kid, to grow as fast as possible, then better tuned to search for sexual partners once we're getting mature, and lastly, more fine tuned to take care of our kids once we got them.
And if there's a mechanism which makes our brain undergo developmental changes along a pre-planned path, then we might also expect that past the age at which we reproduce, there'd be less and less evolutionary pressure to shape that developmental trajectory.
I don't think either that evolution would have much of a reason to cleanly engineer a stable end-state after which development just entirely stops, and leaves you with a well-adjusted, perfectly functional body or brain. That may not be a trivial task after all.
"...the majority of men and women do not officially report themselves as having low levels of sexual desire until they are 75 years old.[8] Many would attribute this lull to partner familiarity, alienation, or preoccupation with other non-sexual matters such as social, relational, and health concerns.[6]" -Wikipedia
One thing that struck me in the 2011 survey was that 90% of LW respondents were under age 38. I'm 57 myself. It seems that often rationality in planning our lives depends on estimates of what values and utility functions we will hold in the future. Has anyone looked systematically at what projected older versions of themselves would think, based on what relevant groups of existing older folks think?
"You'll understand when you're older" is an annoying form of argument. Arguably there's some grain of truth there when a 7-year-old tells you that sex is disgusting and he or she will never ever think it's anything but incredibly gross. But you could explain hormonal changes that as a matter of empirical fact change opinions on that subject in the vast majority of cases. I can't think of anything that dramatic that distinguishes 60-year-olds or 80-year-olds from 20-year-olds.
My dim recollection of studies is that on the whole as people age they tend to be less idealistic, more resigned to society the way it is rather than how it might be, and more constrained by realities of politics and economics (for starters).
I don't presume to offer anything in this regard based on my age, and in any case I'm only a single person (a nihilist when pressed, but one who finds himself happier pretending not to be and working sporadically for rationality, truth, justice, love, and all that good stuff).
When I read of cryonics, what comes to my mind is the escalating costs of health care and (as I see it) the need to curb the development of expensive life-extending medical procedures. Cryonics sounds instead like an extremely expensive procedure. Maybe no one is suggesting it be covered by health insurance, and it's just an option that some people pay out of pocket for. Even so, the "health care is a right, not a privilege" sentiment will mean that if it was shown to work, everyone would want it, and (in my estimation) society would go completely haywire in an unpleasant way.
Now, the substance of the above has probably been discussed elsewhere at length; I raise it is an example because when I was 21 I would have thought of it very differently than I do now.