I agree, someone with a compromised ability to evaluate risk is probably more than capable at doing most desk jobs. However, the last thing we need is politicians who's aging brains have been compromised in evaluating future risks. Putting someone most likely to send scammers gift cards in charge of foreign policy and assessing climate change risks is simply a recipe for disaster.
It doesn't seem all that crazy to demand that the ~300 people running the US not be at an age where mental decline is common.
[1] https://www.scientificamerican.com/article/why-older-adults-... [2] https://neurosciencenews.com/ventromedial-prefrontal-cortex-...