Want to know abt the authenticity of a saying. It might be a hadees or not, not sure:
I come to know that Hazrat Muhammad (PBUH) said that A girl of 12 years will become a grandmother near hereafter (Qayamat). Its in refference of the increase in sex relations between human beings.
Kindly explain,
Regards,

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

We have not come across the meaning that you mentioned in your question about the Hadeeth in any of the reliable books of Sunnah that we have at hand. Moreover, this cannot happen in general as the jurists stated that there are no menses before the age of nine, as stated by Al-Hajaawi, from the Hanbali School of jurisprudence. Al-Buhooti commented on this by saying: “If she (a girl) sees blood before the age of nine, then this is not menses because this has never been seen before.”

It is for this reason that Ash-Shaaf’i said: “I saw a grandmother who is 21 years old.”

Allaah Knows best.