I've seen this several times, yes. So when they're only 19 years apart this can happen. Actually a good friend, who was 39 gave birth 2 weeks after her eldest daughter, who was 20, her 7th child. I think it is ridiculous and I am glad, that I will in my menopause when my daughter is 20.
The days of having all those kids is over. Even with the Mormons. It's rare to see 3 or more families in a ward with 5 + children. It's mostly 3 up to 4 max.
My MIL had TWO children after her first daughter had had two children so there are aunt and uncle younger than their niece/nephew. 25 years later the eldest niece and her youngest aunt (who is my SIL) are pregnant at the same time. The mother of this SIL (who is becoming a grandmother) is younger than me.
My best friends younger sister and her niece are the same age.
My husbands family is a little messed up as an example of never mos in utah in that situation. His mother and grandmother were pregnant at the same time. It was a crime with his mother being 17. His uncle and him have the same father. Use your imagination as to what happened. My husband went years without knowing till last year. His mother doesnt know that his grandmother told him the truth. It was already odd explaining to my family his uncle is our age. Now there is a whole new dynamic to it we are not even allowed to explain. Uncle/half brother.
I knew several people in Utah who had grandkids older than their youngest kids.
When my youngest was at Provo High, we went to a parents' night one time and there were a number of people there with babies. He was mortified. He said "I would die of embarassment if I was in high school and my mother had a baby." I was like "What? High School? That's nothin in Morland."