People who manage to live to 100 don't have much to worry about, as it's a well-documented fact that very few people die after 100.
The Rabbis of the Gemarah knew this joke almost 2000 years ago: There's this discussion going on about how to relate to a missive that has arrived from far away, sent by an old man (this was in pre-Blackberry days). One position is that so long as he was younger than 80, we assume he's still alive when the document arrives, but if he's beyond 80, we can't depend on it. Abaye, however, says that if he was 100, we assume he's still alive when the document arrives, since he has a proven track record of not dying. ("Keivan de'iflig, iflig: since he's already lived long, he'll continue to).
This thread began here.