Divine Angel said:

Someone came up as a suggested friend on my Facebook. I went to school with her. Turns out she’s a grandmother. It’s completely inconceivable that someone my age is a grandparent.

I’ve read that a 19th century Nigerian woman, Mum-Zi, had a daughter when she was 8, and her daughter had a baby at age 9 (to the same father, the chief of the tribe,) making Mum-Zi a grandmother at 17. Mum-Zi was born around 1875/1876.