Yeah go for it im same age as you same height and same weight haha but i ride a 05 250f that is a pretty nice bike, I can handle all the power.
My first bike was a pice of shit and slow when i upgraded to my 250f it was like fuckin faaaast
my friend owns a wr450 and my yz250f smokes em hahaha idk my bike is really fast for some reason
but yeah go with the yz125 great bike reliable and all that stuff, easy to maintain and when u go with one go with 05 or newer cause they got the aluminum frame waaaay better than steel frame
Take care