I know a couple like that. I have a buddy who isn’t that much younger than me (12 years or so) whose mother is 3 years younger than me and whose grandmother is only 10 years older.
His mom is dating a guy his age he went to high school with and has been for the last 5 years or so.
When kids raise kids, there isn’t a whole lot of raising happening.
**edit** guess I’m older than I think. He is 16 years younger than me, she is 3.
Back in the day it was nothing unusual to be pregnant and married at 14 or 15. A hell of a lot better generation than a lot of them now. My Dad was 24 years older than my Mother, so really not a damn thing wrong with that. My parents back then had a hard life and nothing was given to them. Something to be proud of. Careful how you talk, karma is bad, lest you fall into that position as early Grandparents yourselves.