How do i convince my parents to let me get a monroe piercing?

well what i did was explain to them how everyone has different tastes and expresses themselves in different ways, and i told them i really wanted a tounge peircing and they said no at first but then i told them that im pretty much old enought to make my own desicions and that how am i suposed to learn from my mistakes if you never let me make my own........ hope it helps..... goodluck with the convincing :D