Actually, do we even know for a FACT that there are significantly fewer androgen receptors in pre-pubertal hair follicle cells? It would seem like a fairly safe bet, but nevertheless I'd like to see some actual scientific evidence for it. The only study I've ever heard of having anything at all to do with the general level of androgenic stimulus in scalp hair follicles of pre-pubertal humans is the one Armando cited recently, in which a doctor measured levels of androgens in the hair roots of children. But as far as I know, there was no measurement of androgen receptors.