My hub will be 83 in July, he’s sharp, and still doing household repairs and yard work. Other than aches and pain of age, he is NOT SENILE! DOESN’T NEED CUE CARDS. Does take a nap after he does work.
Age is a major factor in senility diagnosis.
But only a factor!
In some rare occasion Alzheimer affect people in fifties or even sooner.
Some hundred year old’s have mind like youngsters.
However, I observed, that most people over 80 are starting to loose some abilities.
They (some of them) can surely function pretty well, but in general, I do not think anybody over 80 should be a president!
Catholic church has a rule that cardinals over 80 are not eligible for vote! It seems to be a good rule to me.