Showing poor mental ability because of old age, especially being unable to think clearly and make decisions. (Cambridge Dictionary)
of, relating to, exhibiting, or characteristic of old age. (Merriam Webster)
Exhibiting a loss of cognitive abilities (such as memory) associated with old age. (Merriam – Webster)
Approaching the end of a geological cycle of erosion. (Merriam – Webster)
If old people become senile, they become confused, can no longer remember things, and are unable to look after themselves. (Collins Dictionary)
Is Clint Eastwood becoming senile?
Herpes Viruses and Senile Dementia: First Population Evidence for a Causal Link.