Very nice piece - thanks for showing it! I have no input as to origin or age, so I'll sit back, watch and learn.
Regarding the material for the hilt, judging from the pics, I am not sure that it is ivory - the pores and nature of the cracks indicate some kind of bone. When bone gets very old and handled a lot, it will sometimes obtain a beautiful warm glow like we see here.
If you'd like, try taking a picture from the pommel-end. A pic from this angle might tell more. What is the length of the hilt, 12-14 cm?
Regarding the possibility of dugong ivory, I still haven't seen an example of this material used for a weapon hilt, and will remain highly skeptical of it's stated use in this way, until presented with evidence of the contrary.
Best wishes, - Thor