At what age do girls start growing pubic hair?

Puberty: Once a girl is making hormones in order to menstruate, then the process is set in order for hair to begin to grow. This will usually occur around 11-12 years of age but may be a bit earlier or a bit later.

It varies: Puberty for girls usually starts with breast buds on average at age 10y pubic hair starts any where from age 10-12 yrs.

Gradual transition: There are thin fuzzy hairs present in the pubic area in girls from early childhood.As the adrenal glands make a subtile change in hormonal output about 6-8 you will see this fuzz darken/thicken and eventually take on the character of pubic hair, but that endpoint is gradual. It can precede the normal marker for starting female puberty (nipple enlargement) by a couple years.