What is the youngest age a girl could give birth?

Once she menstrates: There is no set age it depends on when she starts ovulating or menstrating and when she had sex or exposure to sperm.

Under 10: I believe there are instances where a child with precocious puberty ( a hormone problem) has carried a pregnancy to term & delivered at 8 yo & possibly younger ( i think it was in south america). The youngest I have tended to was 13 at delivery.