When I was around 7 or so. My younger sister had barbies, I used to instinctively cut their hair off and shove the hair in my underpants. I remember making effort to not fully cut off all the hair in order to try and get away with it and hid the hair under my mattress for future use. I did get in trouble with my mother, but she thought it was just me being a destructive boy which I happily went along with!