Hi, Fernando.
Indeed a very nice Yaka sword.
The discolouration of the leather handle is, in my opinion, due to the handling of the sword. It comes from the 'sweat' or 'grease' on the hands of the former Congolese owner. I would touch the leather parts. These things make the piece original.
It's very difficult to put a date on African weapons, but I would think this one is pre 1960's.
Here are the handles of my two pieces :
