Need Help with choosing an mx bike and size questions?

I am 13 years old and about 5'11''and weigh about 135. I am new to the sport and looking for a good mx bike. I was looking at the yz125 but was also wondering if the crf150r expert might be better cause its a bit smaller and a 4 stroke. However, I am worried it could be too small. Also, would the kx100 be too small for me as well. It looks to me that due to my height, im going to have to get a 125cc two stroke unless the crf150r expert is big enough. My major problem is I want to get a bike thats big enough for me but the crf150r expert is the only 4 stroke close to the yz125 in size. I could use some advice.P.S. Im a begginer, so don't recommend anything like a yz250f that il kill myself on

go to your local motorcycle shop and sit on a few bikes such as 125 2 strokes and 150 4 strokes se what feels more comftable and suits you better

The crf150r is a race machine and would be a good size for your age although you may be a little tall, but since you don't have experience you would be better of starting on one of these, but they are still a powerful bike. The yz125 would be slightly bigger and not much smaller than the yz250f. If you think you could manage the 125 then you really shouldn't have trouble with the 250f.Go along to a motorbike dealer and have a sit on a crf150r my son races one and he is 15 although very small for his age weighing only 48kilos and being about 5ft 6 tall.If you are intending to race you would probably be better starting on the crf150r as then you would not be mixing it with bigger kids as once most get too big they move on to the bigger bikes and I know some 14 year old who only race the bigger bikes as they are just too big for the 150