Seriously? How many 70 year old people do you know? Let say you need to urgently take your child to a doctor and can choose between a 30 yo and a 70 yo. What would you do?
Parent cited an experiment that found 70 year-olds to have mental functioning on par with young people. Would you like to argue against the study's conclusion in a meaningful way? Or are you just pointing out that regardless of what is true, humans tend to act in a biased and ineffective manner?
That's a straw man right there. Why would it matter? In terms of the decision making, the one with more knowledge is better. In terms of driving, it depends on if the 70 year old still has the PHYSICAL ability and acuity to drive a car, which is exactly what we weren't talking about.