He's 20, and at 93, She's His Oldest Friend
Article on unlikely warm friendship between 93-year-old Margaret Oliver and Elvis Checo, 20-year-old Dominican-born youth who visits her regularly at Jewish Home and Hospital in Manhattan; photos; Checo, parentless and living on his own, signed up as volunteer and was hired by Oliver's family, although he spends many more hours with her as companion, exchanging conversation and wisdom across the generations (M)