L.M.
My son is 3 and he's had a hairy back since he was 16 months old. He didn't have it when we lived in Calif and the milk was labeled no RBST Hormone. But when we moved to AZ, from 14 months to 16 months he got so hairy. No one in my family has hairy chest/back. My husband doesn't but I think 2 of his bros might. Since he was 18 months he's been back on regular RBST-FREE Milk. And you can buy that from any grocery store and it doesn't have to be organic either. It hasn't diminished but I wish it would fall off. He lost his baby hairiness at 1 but this is ridiculous. He even has a mini light mustache and hair coming out of his nipples.
Both my nieces started their periods at 9 too. I started at 11 1/2 years old(hereditary from an aunt on my dad's side). My mom didn't start til she was 16..but she was in sports most of her life.
My step-niece is 18 now and when she was 12, her mom put her on birth control pills to regulate her period and help with severe cramping. She is a lot more hairier now then she was then. She had hairy legs at 10 years old. It may or may not be the milk. Different ethnic backgrounds have history of body hair too.