My mum won't let me be a vegan?

I was born peskitarian and my mum used to be veggie but lately she has started eating fish. When i was 9 i became veggie. My mum says i can't be vegan until i'm 16 because she wants to let my body grow properly, but i really want to be vegan. I'm a buddhist and i think the way cows in particular are treated is horrible. Any ways to persuade her r advice on what to do? thanks in advance.