My mother took a cognitive test 30 years ago, just before her 70th birthday. She couldn't remember all five words after several minutes and thought her brain was shot. She is now approaching her 100th birthday, still has most of her marbles, but still worries about her cognitive health.
My husband, who was diagnosed with Alzheimer's Disease in 2015, thinks he still has all his cognitive abilities intact. He definitely does not. He cannot remember anything that happened more than ten seconds ago, does not know what year it is, who is the President, or how old he is. It's heartbreaking, but one thing I've learned is that aging is a very individual process. It takes more than drawing hands on a clock to determine if someone is developing dementia.