This map found on Wikipedia shows that people living in tropical climate become senile less, retiring in tropics may make you life better.
I did a search for "Senile" on Wikipedia, it redirected or redefined the word as: Dementia
Alzheimer and other dementias per 100,000 inhabitants in 2002.
The light yellow is the LESS case of dementia or Alzheimer.
Read the page on Wikipedia, it appears to me it would be wise retire in the tropics to extend your minds life.