Hi Martin,
I would think that only laboratory 'tests' could determine the age of the hilt. Bronze and brass seem to be 'easily' aged using chemicals, although I believe the patination produced is only 'surface deep'. The hilt, if genuinely old, has not been regulary handled as there are no 'wear marks' in the patina. The overall condition seems to suggest that it has been in a damp environment, buried in the ground perhaps. But whether this was done to artifically age it or is genuine patina would be hard to assess from pictures.
I've always liked the Benin bronze work.....notice my Avatar
Hopefully Tim may add some thoughts....he has excellent knowledge of 'metal casting' and African artifacts.
Regards David