Gloria Campbell retired from her job in academia around five years ago, but she hasn't stopped working.

"I believe that people should ... never fully 'retire' from life," she said.

For many years, Campbell oversaw a college program teaching engineers how to write, and she continues to earn part-time income by teaching classes and editing books. Between that income, Social Security and a small pension benefit, she lives on around $2,600 a month.

Campbell's husband passed away a year and a half ago, making her the sole supporter of her disabled son, who lives with her and is unable to work.

"Supporting the two of us is a stretch, of course," she said. "So what I do is basically watch my income, own my home, and I am very very careful about what I spend."