This Benrus model is also one of my favorites; I actually have three of these (two of them are identical to the one in the photo, while the third is slightly different - the days of the month are listed in an interior circle as opposed to an outer one. I'm quite certain all three use the same movement.) Determining the age of these watches is a bit of a challenge. Like you, I have not come across any database on Benrus serial numbers. Nevertheless, in this instance there's a way to approximately date the watch, based on the patent number. The cited patent (2,581,268) was granted in the US on Jan. 1, 1952, so your watch (or at least the case) was definitely manufactured after that date. It seems that Benrus built these watches over a long period of time. One of the watches I have does not have the patent number listed on the back (only the serial number), which implies that it was built before the patent was issued. The filing date for the US patent goes back to 1949, but it seems the original Swiss filing dates back to 1946. Unfortunately I have no idea about when Benrus stopped manufacturing/selling this model. I will look up the serial numbers on the watches I have tonight; I doubt, however, that they will provide significant additional information.
Regards,
Mufit