Among the ranks of the Fortune 500, just 11 corporate chief executives have remained in their jobs past the age of 70. Of the 100 members of the U.S. Senate, by contrast, 22 have reached septuagenarian status -- and seven of them are either older than 80 or will be before their terms expire. Of the U.S. Supreme Court justices, only one -- Clarence Thomas, 56 -- is not old enough to collect Social Security. These numbers make it plain that the top tier of the federal government remains the most welcoming arena in American society for people who want...