Jennifer Williams says she often feels like the oldest person on her block. When the 52-year-old corporate communications executive sets off for work in a suit, carrying a briefcase, with her hair in a bun, she is usually surrounded by young people with tattoos and rainbow crocheted skull caps. "It's like mom is coming in for a visit," she says.

That doesn't bother Ms. Williams. In fact, such diversity is exactly what she was looking for when she bought a condo in the Williamsburg section of Brooklyn two years...