code: def age(self):
          
          if not self.birthdate():
              return -1
          adjuster = 0
          today = date.today()
          birthday = self.birthdate()
          if today.month == birthday.month:
              if today.day < birthday.day:
                  adjuster -= 1
          elif today.month < birthday.month:
              adjuster -= 1
          return (today.year - birthday.year) + adjuster
docs: Returns the user's age, determined by their birthdate()