Well, since kids grow up so quickly and the aged are living longer so that 70 is like the new 50, it is only a matter of time before the generations criss-cross each other and the kids are older than the grandparents and the grandparents are younger than their children, as long as current trends continue.
Well if a woman gets married at 19, and her child has a baby at 19, there you have it. I would imagine it is quite common in the chassidish communities. Not young 30’s perhaps though.
I know someone (Sefardi) who got married when she was 16, and her eldest daughter got married when she was 17. She was a grandparent by her mid-thirties.
well think about it, some chassidish people get married when they are 18, so if they do then have a child after 1 year, they grow up to 18 get married the paretns are grandparents a year later at the ripe old age of 38!!!