Last Days of Ptolemy Grey  by Walter Mosley
Ptolemy is 91, a recluse living alone and falling fast into dementia when this story begins. Confused and scared, his apartment is filled with filth and bugs. A family friend, Robyn Small, 17 years old, comes into his life and both find needed friendships. Robyn helps Ptolemy clean up his apartment. A reinvigorated Ptolemy volunteers for an experimental medical program that will restore his mind, but at hazardous cost: he won't live to see 92. Mosley's depiction of the indignities of old age is heartbreaking and Ptolemy carries off these indignities with grace and decency.