So why not start your project with existing information about possible personality types and motivations you need to accommodate—whether you refer to astrological profiling or a more traditional psychological study—and avoid the impulse of putting a face to them if you can. To follow, use your research time to discover real scenario specific behaviors and, later on, validate your solutions with users as you usually would. Whatever you do, don’t assume that simply asking your users their date of birth will count as a user test.
That will never work, especially if your client is a Virgo.
UX Lead at Ebury and graduated as a Computer Engineer at the University of Granada. In the past, I've worked as a teacher, consultant, and developer. Designing valuable technology for people is what I enjoy the most.