The latter part of life, the part of life after one's prime.(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "old age" in a sentence
"A better ruler was Guido Lucio, who in his old age in 1389 was thrown into prison by his sons, where he ended his days."
"Afflicted with Diabetes Type I since the age of eight, Jen was taking ten different medications at the ripe old age of twenty, including insulin, as well as meds for general pain, neuropathy, and fibromyalgia."
"He escaped annihilation with Crassus at Carrhae, then governed Syria extremely well at the ripe old age of thirty."