Depends on who is talking, my grandfather ate healthy and exercised nearly his entire life and lived to be 96 before he started getting Alzheimer's and died a few years later.

I think most people would consider my grandfather to be a near optimal outcome in terms of lifespan and keeping your mind nearly intact until you are very very old. The number you are citing isn't even average lifespan in US for instance (78 currently). If you take out most of the things which are out of our control from that average, or things which cause disproportionate amounts of negative entropy on your body and recalculate it (things like homicide, suicide, accidental death, people who smoke profusely, people who drink to excess, people with severe mental health issues, etc etc) the number is much much higher.

Yes, 72 is late onset. I don't understand why OP is cynical. There is a big difference between getting Alzheimer's at 50 and 72. If exercise and other measures give me an extra 22 years of productive life, I'll do them, whatever they are