Sure, you'd be able to handle it. Some people recommend TTR, KLX, DRZ 125s or a CRF 150 because they are smoother, but an 80 isn't impossible. You will just learn throttle control a lot quicker--and it will have much better suspension. In fact, at 5'7" you will probably outgrow it pretty fast--I am 5'7" and feel totally cramped on an 80. You'd be tip-toe on a full-size bike (I am) and maybe if you shaved the seat foam down, you could look into that for the future. Have fun and keep us posted.