Mine came in naturally at puberty. I was raised in an all female household and it just seemed natural that I should grow breasts like the older girls. Never thought any different until the boys started grabbing them!
The only thing I do to keep them firm and pointy is eat healthy and do exercises to keep my pectoral muscles strong. I have a 40C rack and figure if I have to pack them around all day I might as well have fun with them!