The SWMBO = She Who Must Be Obeyed has been around long enough that I thought everyone knew it.
POSSLQ = Person of Opposite Sex Sharing Living Quarters (pronounce it "poss el cue") is one I've never cared for much, because I first encountered it in a very stilted and badly written "socialogical essay." It probably dates at least to the 60s.
The other one might encounter is SO = Significant Other. Although some have objected that it refers to a "shack up" mate, I've found it most often used by married couples when in the presence of other couples of uncertain situation, as a matter of politeness when explanations are unnecessary. It seems rather neutral to me.
As one with some vicarious experience of older women, I would interject that at my last high school reunions, age had done a bad turn on quite a few - of both sexes. But the ones who still looked good looked VERY VERY good. The funny thing is that those who looked the best seemed also to be the ones willing to enjoy and be happy with themselves. Maybe the others just forgot how(?).
(As there are very few older than me still around, it's difficult to comment on older older women. My grandkids are deteriorating noticably.)