I agree with Maddojo, you should learn to safely ride the bike first because it can become quite dangerous when jumping etc. For your weight and height, i would suggest a Yamaha yz125 or a tt-r 230F. Depending on what you want to use it for. I personally think you would have loads more fun on the yz125, as it was my first bike. The tt-r is a great bike for beginners, but the yz provides more acceleration and is better for later on. Although if you want a bike that is really reliable, go with the tt-r. It is a four stroke and so it takes straight gasoline instead of mixed fuel, and it requires a lot less maintenance than the two stroke yz. Hope this helped with your decision!