Girls hitting puberty earlier? Is milk to blame?

So I'm not quite sure. It's pretty certain they don't overlap, but probably inextricably intertwined.

Puberty is when your pituitary glands release hormones to accommodate for your growth spurt, your mental development, etc. Males get the hormones sent to their testes to release testosterone. Females get estrogen from their ovaries which enables them to menstruate. I don't get why the whole concept of puberty is complex, it's both a mental and a physical process that you go through.