I can see some common ground with you on age restrictions. We have an age restriction MINIMUM (35) and it only makes sense to have one for being too old. We arbitrarily said 35 years was the minimum, we would have to agree to arbitrarily set a maximum age. A person can be too young and inexperienced to run for president, but he can't be too old AND cognitively impaired?
We also agree that Trump lies and exaggerates quite a bit. I don't mean to justify his lying (especially since I've called him out on this site), but there isn't any linkage between "lying/exaggerating" and "being senile". Trump isn't lying/exaggerating BECAUSE he's mentally impaired... He's lying/exaggerating while being in relatively good mental health. He has taken those cognitive tests as well.
You could make the case Trump ought NOT to lie or exaggerate and I'm with you... but to use that to illustrate his cognitive decline is extremely disingenuous.