Well, I started on a ninja 500r and while their have been times I WISH I had gotten a bigger bike their have been times I'm very thankful I only have a 500. You really don't need a SS 600cc bike for the first couple of months your riding. After that then yeah you should be ok but those little mistakes you make during your first couple of months on the road can really get you into trouble fast on a big bike. My advice from a 1/3 season vetren is to start on a small bike, used, cheap and sell it in your second season and get a 600 and go from their. I've been down twice on my bike and I'm really happy that it wasn't on a brand new or any bike other than my used starter bike that already had some blemishes on it.

Best of luck to anyone shopping for a bike...it's a hard decision but one that really pays off when you take that first WOT run and a few months later when you go into and tight turn and drag your knee comming through it....nothing more exciting.
But start on a used bike....I'd suggest an sv650 or ninja 500....250's are a little small for driving on the interstate