For me, the main issue isn't the increased risk of cognitive decline, it's the fact that I share very few life experiences with people born before the invention of color tv, and someone who has another 5-15 years left will be less impacted by policy decisions than someone who's going to be around for another 50-60 years. Octogenarians are not representative of the majority of the population and, in a representative democracy, I think that is important consideration.