Hey I'm just turned 14 and I'm on my dads name.have you ever thought of getting a YZ205F lowered?Also,You might want to think about a CR250.I was on my KX100 when I was 12-13years old and then my dad got me a 2002 CR250.It's one of the best bikes I've owned because its LIGHT,has tons of low-end and is the perfect motocross/off-road bike.I'm only 5'3 and can get it started and ride it well.It's not lowered because it's the perfect size.It would be the perfect size for you with your hight and weight.You might need soft springs and that would make it even lower.With the CR250 you can go almost anywear.All you need to do if be easy on the throttle beacuse it has tons of power.For you a KX/RM100 might not pull you everywhere.One the track with my KX100 there were places when I needed more power.Same for off-road.I think a CRF250X(the off-road CRF bike)would be a good choice but it will coast about $5899+ and wont come out till winter of 2003.I hope you find the perfect bike for you.