The condition is generally called "dementia," which does not mean "crazy." Rather, it is a progressive decline in cognitive function, which may have a variety of causes. Old age is only one of them, but it is more common now as people generally live longer. My mother-in-law (who is now 97) has been there for several years now, with it getting gradually worse, and my father (86) is starting the same process.

Herself (the occupational therapist) works with older people a lot, and says that this is a very common problem...she has patients whose birth language is Spanish or Navaho and they often lose the English they learned later in life...her solution has been to learn some Spanish and Navaho. My own way to deal with it is with patience-if they ask the same question they did an hour before, answer it the same way you did then; don't say something like "I told you that, Mom," because she will just not understand. Sometimes each moment is a discrete one...there is no memory of what happened 5 minutes before...because the connections in the brain just aren't working right.