>As for your women past the age of menstruation, in case you do not know, their waiting period is three months, and those who have not menstruated as well. As for those who are pregnant, their waiting period ends with delivery. And whoever is mindful of Allah, He will make their matters easy for them.
Surah 65 verse 4
You wait 3 month before expelling your ex wife in case she is pregnant. "and those who have not menstruated as well" mean pre pubescent girls, you can look at the tafsirs
There's no age minimum to marry in islam