The elderly are not more in favor of Social Security and Medicare than the rest of the population. Seniors strongly favor these programs, but so do the young. Contrary to the SIVH-inspired bumper sticker “If men got pregnant, abortion would be a sacrament,” men appear a little more pro-choice on abortion than women. Compared to the overall population, the unemployed are at most a little more in favor of government-guaranteed jobs, and the uninsured at most a little more supportive of national health insurance.

This is an absurdly narrow definition of self-interest. Many people who are not old have parents who are senior citizens. Men have wives, sisters, and daughters whose well-being is important to them. Etc. Self-interest != solipsistic egoism.