Age has nothing to do with it, really, Richard. My mother developed dementia at about age 67 and died this past February at age 72, totally out of her wits. You have to judge by her facilities rather than her birthday.

Punkfolkrocker, if you feel your mother's decision making abilities are starting to go you should step in and have a heart to heart with her first. See if she's open to having your help. Has she started making silly decision or had money go missing with no explanation?