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.n a study of seventeen thousand girls, it was concluded that girls do not need to be evaluated for precocious puberty unless they are Caucasian girls showing breast development before age seven or African American girls with breast development before age six.