I've encountered this with friends in their late 40s, complaining about their parents' life choices after losing a spouse. I asked them how would they feel if /their/ children acted like that toward them. I also asked if they felt their parents no longer deserved to be able to choose for their own lives and their own happiness.

Sure, maybe at some point we all end up having to care for our parents toward the end, but isn't it better that we stay out of their love lives in the meantime?

I speak as someone whose mother is in her 60s and recently moved in with her 70s something bf... to which I told her that I'm grateful she's happy and found someone who she has fun with.