I suggest you go sit on a Honda CRF150F, CRF230F and Yamaha TT-R230. My girlfriend recently bought a TT-R230. She's 5' 8" and a beginner. The seat height is 32.5", I think.
I think you are too heavy for a KX100, and a quick revving MX bike may not be the best thing to start with on dirt.
I think you are too heavy for a KX100, and a quick revving MX bike may not be the best thing to start with on dirt.