Female Puberty and Sexual Development of girls. Stages of puberty in girls / females. Sex development and puberty in females and girls. Sex organ development, stages, phases, early or delayed puberty. Breast Development (Thelarche)The first visible evidence of puberty in girls is a nickel-sized lump under one or both nipples. Breast buds, as these are called, typically occur around age nine or ten, although they may occur much earlier, or somewhat later. Changes during puberty happen to every girl! Here’s everything a girl can expect, from milestone to milestone. Visit jj-rey.net and get more info on puberty.