OP, I had EXACTLY the same experience with my late parents! It manifested in different ways, as they were never political, but they became utterly insufferable, really right-wing socially, and it went on and on and on.
In their fifties, they were very different. They never once pressured me about marriage, or kids, or anything like that, and they were very encouraging and supportive of my career.
Fast-forward to their mid-sixties. They had become grandparents via my sister and I had got married. Oh my God, it was like beings from outer space had replaced them. They suddenly became like something out of 1750. I phoned a lawyer once about some issues we were having with our block of flats, and my mum told me that that was something my husband should sort out! And I have a BA and an MA from Russell Group universities and a career, and suddenly they were treating me like some bimbo. I once hammered a nail into the wall in a cupboard to hang up the clothes dryer, and my dad asked me why my husband wasn't doing things like that.
They went on at me to cook my husband's dinner, and to clean, and oh my, the PRESSURE to have children went on and on and on. The comments about how selfish people are who don't have them, how they spend all their money on themselves, and my dad even curtain-twitched about a woman who lived about ten houses away and the different men she had staying over! While you do have to drive past that house to get out of the cul-de-sac, I would never, ever, in a month of Sundays notice what cars were parked in that driveway or when.
They got older, retired, became grandparents, and changed into a pair of socially conservative complete nightmares who never stopped trying to impose their 1950s views on me and try to make me conform to that stereotype of a housewife. And they were NEVER EVER like that before.
I can only think that this is some very weird, deep psychological response to entering the final stretch of their lives. Such a pity as it really strained my relationship with them in their final years, and I did not enjoy their visits.