I don't know what dirt bike to get?

When I was 7 my dad bought me a Honda XR70. It was always a great bike but I am now 15 and want a bigger bike. I am 5'7 and 140 pounds. As of right now I have $800. Someone offered to sell me their 2004 Honda CRF100 for $750. But I'm not sure If I should get that or a 150. I don't have a job so it would be hard to save up. But I think if I put some money towards it my parents would buy me a 150 for my sixteenth birthday but thats not for nearly another year. I'm not sure what should I think about doing?