It should be based in science. IMO, on evidence for when the brain starts to age in a significant way, and supplemented individually based on a robust battery

It should be based in science. IMO, on evidence for when the brain starts to age in a significant way, and supplemented individually based on a robust battery of tests that represent cognitive fitness (something more demanding than n-back and stroop tests). Unfortunately, I think fantasies about living forever and politics around ageism will prevent this from ever being implemented in our lifetimes.