At age 36 I already feel too old at LW meetups.
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).
There is a moment in one's life where their quality of life starts depending on money they make. I'm not talking about having your first job -- if you live at your parents' home, they give you food and bed, and you are free to spend your money as you wish, you are not there yet. Even if you pay all your expenses at market rate (though you probably get a huge discount), you are only halfway there if your parents provide you safety; if they would be willing to pay your checks for some period if you'd happen to lose a job etc. I am speaking about a moment where if your income disappears, your quality of life would drop dramatically. This moment is IMHO what makes the large part of the difference.
I have seen this at the university -- some people went there directly from a high school; some of them failed, had a job one year, and the next year succeeded to get at the university, keeping a part-time job. Despite the same biological age, the attitude difference between these two groups was huge. The first group was always interested in talking and having fun, the second group was focused on problem solving.
Having a metaphorical sword hanging above one's head changes things. A rather big part of my time has to be spent making money, otherwise I lose my home. I don't have enough time for my hobbies; and even when I have the time, I often feel too tired to do anything meaningful. Because I can't do the things I want, I care even less about other people, except for very close friends. A lot of this would probably change if I had more free time (I feel my priorities shifting on weekends and vacations), but I can't manage to have more free time for a longer period. And I don't have children yet, so I suppose I will have even less free time in the future.
Other part of the story is that age brings experience -- this is not automatic, but if you have tried a lot of things, then you statistically have more data about things. When I speak with younger people about their idealistic ideas, seems to me that they are missing the data, and they don't even realize they are missing something important. (If saving the world is that simple, do you think you are the first smart and altruistic person to ever think about it?) Maybe it is not about idealism, but about expecting simple solutions to complex problems. If you would measure idealism not just by words, but by long-term persistence in face of obstacles, then maybe the difference in idealism would disappear.
Sounds like a good argument for assembling your own safety net (enough savings to last several years) early in life, even at the expense of the other aspects of current quality of life (living in a smaller apartment, avoiding luxury spending etc.) Dependents (spouse+children) might make this impossible though.
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.