senile
When he thought someone noticed his mental slips, he would smile warmly and blame senility.
There is a world of difference between wavering concentration and actual senility.
He has a short memory when it is convenient, or is this senility creeping in?

SMART Vocabulary: related words and phrases

The elderly
advanced
advancing
age
aged
ageism
crock
gaffer
geriatrics
gerontological
gerontologist
gerontology
golden oldie
infirmity
old people's home
old-timer
oldie
pension fund
pensioner
the gray dollar
the grey market

You can also find related words, phrases, and synonyms in the topics:

Mental illnesses