Old age is changing. So should Social Security.

Abolishing age as a standard of fitness would be fairer than simply raising the eligibility age. We've already taken steps in this direction. In 1983, when critics complained that raising the retirement age would abandon people who could no longer physically handle their jobs, a Social Security reform commission pointed out that the program's disability benefits would fill in the gap. And in 1986, Congress removed the upper age limit on people protected by the Age Discrimination in Employment Act. If you're healthy enough to do the job, age doesn't matter.

The final objection to both proposals is that Social Security is a trust fund; you made your deposits, and you're entitled to your withdrawals. But if you think the reason you'll live longer than your grandparents is that you're a better person, think again. Programs such as the ones Congress debated this week—Medicare, public sanitation, and biomedical research—bought you longer life and better health. Maybe, instead of asking what your country owes you at 65, you should ask what you owe your country.

A version of this article also appears in the Outlook section of the Sunday Washington Post.