Legal Question in Elder Law in California

I am not sure if I understand your question correctly, but I think you are asking what determines if a 75 year old is competent. I think this is a question for a psychiatrist. You need to have the elderly person evaluated by a psychiatrist and then an official determination will be made. There are signs of incompetence, which may include inability to take care of oneself, inability to take care of ones own finances, Alzheimer�s etc, but these should be evaluated by a medical professional.

Her competence is 'evaluated' or 'judged' by observation and testing by doctors or others. If not competent to take care of herself, she needs a guardian or conservator.