Must one make up prayers missed before the age of eighteen, knowing that menstruation began at the age of thirteen?

Neglecting prayers out of laziness is a grave sin; indeed, some jurists have even considered it an act of disbelief (kufr). The questioner must make up the prayers she missed since puberty, estimating their number. The signs of puberty for a woman are five: ejaculation (emission of fluid), growth of pubic hair, menstruation, pregnancy, or completing fifteen years of age. If the first three signs do not appear before the completion of fifteen years, then her puberty is marked by reaching that age.