senility

noun
  1. 1

    Senescence; the bodily and mental deterioration associated with old age.

  2. 2

    The losing of memory and reason due to senescence.

    โ€œHe was entering his years of senility and not liking it a bit.โ€

  3. 3

    An elderly, senile person.

Antonyms

Source: https://en.wiktionary.org/wiki/senility