docs: def get_age(self, **kwargs):
          """
          Returns the particlees age (how long it has been forced) in a variety of units.
          Rounded to 8 decimal places.
  
          Parameters:
              units (optional) = 'days' (default), 'hours', 'minutes', or 'seconds'
          """
          try:
              units = kwargs.get('units', None)
              if units is None:
                  return self._age
              units = units.lower()
              if units == "days":
                  z = self._age
              elif units == "hours":
                  z = self._age * 24.
              elif units == "minutes":
                  z = self._age * 24. * 60.
              elif units == "seconds":
                  z = self._age * 24. * 60. * 60.
              else:
                  raise
              return round(z,8) 
          except StandardError:
              raise KeyError("Could not return age of particle")