Size isn't all that important. Balance, attention, and experience are. I'm 5'11" and recently dropped from 215 to 170 lbs. My 500 lbs Hayabusa and 700 lbs VTX-1800 never felt so good. I have a friend who’s 5' nothing and just a shade over a hundred pounds that handles a big CBR1000 like a toy.
However, since you are brand new to motorcycles I strongly suggest you start with a light, non-plastic bike. Motorcycles can be very heavy, and once you get them beyond their balance point they are very difficult to stop, no matter how big you are. You are very likely to drop your first bike. Look for something like a GS500, or EX500 as a starter bike. Plenty of power to keep you interested, good handling, but light enough to help cover for small errors in judgement.
Also, take a Motorcycle safety course. Highly recommended by most riders.