My parents won't let me ride MX (motocross) how can I persuade them?

I am 14 years old, female, 5 foot 5 inches and weigh 7 stone. I am willing to pay for the bike out of my own money and will also pay for the gear/lessons as well. I love Guy Martin programmes and he did an MX jump and it inspired me. I enjoy mountain biking and there are transferable skills. I am an adrenaline junkie who isn't scared of much and I love speed. Neither of my parents ride or like motorbikes.  

2017-04-11T00:37:33.809Z