Im 14 and I have a 2001 kx100. It is a great bike. You seem perfect for the bike. I have outgrown it but your quite abit smaller than me. The 125 will be a bit big for you. The 100 is a great seperation between the 85 and 125. I will recamend this only if you can handle the power band and light weight of the bike. A for stroke In my opinion sucks. I love the power band to come on and just rocket the bike forward. You may not you just have to try it to find out