This style with a slash neck with ribbing across the top, and drop shoulders, was common during the 80s. The label typography and its washing symbols, looks a bit more 70s, but I still think the sweater is 80s, perhaps early the decade.
Here's an 80s knitting pattern for a similar shape (on the right) - note the same slash neck, and ribbing that goes right across the top, as far as the top of the dropped sleeve.
It reminds me of the sweater worn by Banarama in the mid 80s pop video 'Venus', certainly the shape of it. Difficult to tell from the video quality what kind of fabric is was.