Right, good, I'm glad to know that 'reaction time' is a key part of the presidency.
Again, if an employer said 'that woman was more skilled, but I chose the man since she may get pregnant and I'd immediately have to look for someone else', you'd say that was absolutely and completely wrong.
You, as an employer (a member of the electorate of the United States of America), are now saying 'that older person was more skilled, but I chose the younger one since the older one may get dementia and I'd immediately have to look for someone else', and now you're defending this?
These are completely incompatible positions. You cannot justify them!
I'm not in any rush to elect an older candidate. I don't have any specific preference or aversion over age - if anything, I would like it if more younger politicians rang, so that the political class could be more representative. What I do find disturbing is the rush to disqualify older candidates purely on the basis of age itself.