Under 6 foot, and under 200 lbs. Had not ridden a bike between 1984 and 2002. Bike in 84 was a little kawasaki (but I was smaller then too!).
Bought my '02 RK without test driving.... and went back to pick it up.... jumped on it in the parking lot and first thought was "This bike is too big for me"...
I let my original Driver's license / moto endorsement lapse, so I had to written and road test again. Failed the first time.... then passed my State's road test ON MY RK!
Immediately after that took my safety course.... and handled the little bikes like a pro... knees got in the way on sharp, slow turns, but that was actually beneficial, because it taught me LOTS about balance and stability.
6 years later.... I wouldn't trade the RK for anything.... but don't think I could RIDE a smaller bike.
My ONLY suggestion about buying a "training bike".... look in the paper for a POS... beat up, old, and cheap. Make sure it is safe and mechanically sound. Buy it, get 3 to 5K miles on it, learn how to do tight turns, slow stuff, panic stops, etc. on IT, rather than on an expensive, long term investment with lots of shiny chrome!
After you are SUPER comfortable, buy your fatty.... and sell the old lil bike to someone else that needs a lerner bike... you'll probably get all your money back that you originall paid for the lil bike!
Lastly, insurance for a smaller, lerner bike is less... smaller engine, less value, etc. PLUS, if you ride that for a year, then your 2nd year of insurance drops dramatically (cuz you survived the first year...lol). Then the Fatty ins is more reasonable.
good luck!