Hi Thijs, my first post here & I might be able to help you ID your bass.
First of all, Orfeo will be an importer's brand name - the Japanese factories in the 70s exported under many, many different names, usually chosen by the purchasers in the countries they were exported to. Even Ibanez was only ever a brand name, not a factory!
Age-wise, it's quite difficult to tell, (although some serial numbers show the date of manufacture) but I'd be inclined to say late 70s. A couple of things make me think this: early Japanese basses (and guitars) tended not to feature a position marker on the 19th fret - they would stop at the 17th. Also, the nut and tuners are the correct P-bass type - early copies often had a Gibson-style nut, with either a chrome or white plastic truss rod cover. Tuners were more usually medium-sized, with closed backs & cast, square-ish keys.
The neck plate might give a clue as to which factory built it - if it features the "Made In Japan" text stamped on the lower part of the plate, these are commonly seen on guitars from the Fujigen Gakki factory, while if it's on the upper half, Rokkoman/Maya is a possibility. If the plate also reads "Steel Adjustable Neck", then this is often seen on guitars from Matsumoku. A 6-bolt plate is connected to the Moridaira factory.
None of this is "hard" evidence - there's very little record of the 70s Japanese guitar industry, and with so many factories (the ones I mentioned are the better-known ones - there were many others) producing basically identical instruments, it can get a bit confusing!
Anyhow, hope this helps, and if it doesn't, hopefully you at least found it interesting!
Jon.