According to The Record, Mom did know what she was talking about:

"Eat your spinach."
How many times did you hear that while growing up. Or the vegetable may have been broccoli, green beans, squash or peas. In any event, mom was once again proven right, according to new research on vegetables and aging.
The study, conducted by the Rush Institute for Healthy Aging at Chicago's Rush University Medical Center, found that eating vegetables appears to help keep the brain young and may slow the mental decline sometimes associated with growing old.
Older people who ate more than two servings of vegetables daily appeared about five years younger at the end of the six-year study than those who ate few or no vegetables.