I don't think this applies to all 80 year olds though. Some of the smartest, most open-minded people I've met have been 70+ year old university professors. These are the kind of people who retired, and then came back to teach because they were bored. It's definitely possible for humans to retain their critical thinking well into that late stage of life, but I'll grant you that most who make it to that age don't seem to manage it.
I can only hope that if and when I reach that many decades on this planet, I'll still have the kind of clarity of mind to not get stuck on 'autopilot'...