old age; senescence
Refers to the stage of life after middle age, often used in medical, psychological, or sociological contexts.
Even after entering old age, I want to take care of my health.
高齢期 is a similar term meaning 'advanced age period', often used in gerontology and social welfare contexts.
老年期 refers to old age, the life stage opposite to 幼少期's early childhood.
Compound of 老年 (rounen, 'old age') + 期 (ki, 'period, stage').