But, for goodness sake, don't make her cute. Most of us women over the age of 50 aren't that adorable or gray-haired today. Think Lauren Hutton as the grandmotherly burglar or Elizabeth Dole. Maybe your Dole figure is breaking into the Watergate Apartments for information that will help a charitable organization like the Red Cross. People aren't cardboard.
Character is too important a story element to let go at combining disparate elements.
Even if you use non-stereotypical outer aspects of those who populate your tales, please also remember to give these beings some depth. Assuming that you, as a real human soul, have certain musings and motivations beyond the superficial, so should your story's cast. Make us believe that there is a strong enough reason here. Give us a mindset that will chill us, if you like, but don't allow the readers' eyes to roll upward in skepticism or disgust. People are interesting.