Pubey does NOT occur before the age of 8 years because:
Pubey and regulation of its onset During childhood the hypothalamus does not secrete significant amount of GnRH because during childhood, the slightest secretion of any sex steroid hormones exes a strong inhibitory effect on hypothalamic secretion of GnRH. But at the time of pubey, the secretion of hypothalamic GnRH breaks through the childhood inhibition and adult sexual life begins.
The hypothalamus does not secrete GnRH in a pulsatile manner
Inadequate synthesis of gonadotropins by the pituitary
Gonads are unresponsive to gonadotropin
Positive feedback action of gonadal steroids on pituitary
Female Reproductive System