Today we have a bit of a puzzlement. (Nothing new there I know.) This is an unknown couple, surprise, surprise. Obviously there is a man on the right and a woman on the left and there is a possiblity of a great age difference considering his hair is 100% snow white and she doesn't appear to have a touch of gray or a wrinkle anywhere to be seen. Not necessarily accurate since everybody balds, wrinkles and grays in their own time. Here is where it gets a little tricky. Since you can't see their entire outfits nor is there a background you haven't very much go to on. Let's break it down a little more.
If you look at her clothing you will see that her sleeves are starting to puff out at the top. This started in the 1890's or so and I found almost identical sleeves in the fashion plates of September, 1893. The gathers are on the same plates. None of the plates however have the women wearing jewelry. If you look down towards the bottom of the image you will see the chain of a pocket watch or possibly some other form of jewelry.
Timeframe: I basically said all that to say I haven't a clue when this picture was taken. Due to the lack of any solid information and conflicting clues my best guess is in the 1890's but pretty much anything is possible.