Placenta Posterior Low meaning your placenta position is at the back and is on the low side.
You should avoid sexual intercourse, carry heavy thing, strenuous exercise.
Don’t worry too much for now, it will likely move up as you progress with your pregnancy. That is what happen to me.
And position of the placenta cannot determine baby gender; that being said, it is common for woman to carry a boy when their has placenta posterior low.
But suggest to wait for the detailed scan in trimester 2 to determine the gender of your baby.
Take good care and God bless tot and baby!