I think it is 1950s/60s, and I'd say a size 12.  

It has clearly been well loved and well worn - there are several worn areas, one of which has been disguised with a patch sewn onto the lining behind it!  One button missing on the jacket, and the hooks on the 'hook and eye' fastener on the skirt have needed repair. The lining also needs restitching around the armholes and on the vertical back seam. I hope the pictures show you all the details.

Has been in a cupboard (in my aunt's house) for many years, so is rather musty and needs a clean.

Overall not in a very happy state, but an item I think is worth restoring to it's former glory by someone who can give it the attention it deserves