This quotation comes from a review in The Economist of Out of Time: The Pleasures and the Perils of Ageing by Lynne Segal. 

“The great secret that all old people share,” observed Doris Lessing, a Nobel prize-winning author, at 73, is that “your body changes, but you don’t change at all.” The effect is confusing, she explained—no less so, surely, now that she is 94 [until her death two days ago]. Old age often brings loneliness and sadness, but also a greater appreciation of the transience of all things—a thought that can be moving, not just depressing.