As human life extends, it no longer makes sense to think of 65 as “old age.” We live in the age of the 65-year-old marathon runner, the 65-year-old rock star, and the 65-year-old new father. (At today’s pace of technological improvement, we may soon be surrounded by 65-year-old new mothers.)

Old age comes later now. But when it comes, it changes people in the same way it always did. Women begin radically to outnumber men. (In 2010, the older-than-80 population included 4 million males and 7.2 million females). Personal savings are exhausted. (Average net worth drops by 25 percent between age 65 and age 75.) Dependency rises. Attitudes to government change.

The older you get, the more you appreciate Social Security and Medicare …

… and the more you mistrust proposals for reform that might affect current recipients. In 2009, 43 percent of people in their twenties were open to reforms in entitlements that might touch those now receiving Social Security and Medicare; only 27 percent of people in the strongly conservative groups older than 65 would consider it.

As yet, few published surveys break out the differences between people in their sixties and eighties. Working politicians notice it, though. As one very successful political operative told me, “The No. 1 concern of every voter over 80 is, ‘Will my check arrive on time?’”