it's too young biologically NORMALLY, but in rare cases, a girl may hit puberty young around 5.
So by the time they are 9-10, they would look much older for their age, such as 12-13. See this video at 2:10. Girl is 9 yet clearly has the body of a 12-13 year old. Even the narrator acknowledges early puberty may make someone look older 4-5 years older than the average.
The mother also mentions how her sisters are 3 years older than her, yet the 9 year old is still taller and bigger than her 12 year old sisters.
View: https://www.youtube.com/watch?v=HHfj_IJ464U
Even speaking from personal experience, My 5'4 11 y/o sister has a wider frame than my 5'3 16 y/o sister, as such, I have no doubt saying she would handle childbirth easier than my other sister. Meanwhile, my 10 y/o sister is 4'8 and looks like she's 8.
No those villages don't do it because it is RARE for a girl to be developed by 9, but it is not IMPOSSIBLE for a girl to be developed by 9.