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'

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")