You're completely overlooking the fact that, a rapid demographic shift such as say, doubling life expectancy within 50 years, would lead to massive social uphea

You're completely overlooking the fact that, a rapid demographic shift such as say, doubling life expectancy within 50 years, would lead to massive social upheaval, regardless of voting preferences. There would be huge shortages of nursing homes, care workers, early bird dinner spots, seniors cruises, etc. (sorry, had to throw some jokes in there). Social security benefits would collapse. Retirement age would absolutely have to change, or we'd simply have massive unemployment (imagine if people lived to 120 but couldn't find work for the last 50-60 years of their life). Thinking about voting preferences is really just rearranging deck chairs on the Titanic. Society would either collapse or see massive shifts simply due to physical needs, well before voting preferences became the dominant factor.