It would really depend on where you intend to ride the bike.
If you are going to be covering a lot of open highway then I would not suggest a sport bike.
But if you are not, then the 600 makes an excellent starter bike.
It really doesn't matter how big and powerful the bike you are buying is, and the 600 isn't what I would consider a powerful bike. It is really up to the rider to make the determination as to what they consider to be too powerful and 600cc is a good place to start. I'm sure you will soon want a larger bike soon after. The 750cc is also a good starter bike in my book as well...
This is really a decision that is up to you to make. Seeing as you will be the one riding it, you should go have a sit on one at a dealership to determine if it is at least the correct height/comfort level for your riding position.
It is also a really good idea to take a rider safety course, not only to lessen your chances of dying, but it also saves on your insurance as well.
Pay attention to hidden costs when purchasing a bike as well. A decent helmet, set of riding gloves/boots can set you back a hefty sum. See if you can't get the dealer to throw them in on the deal when buying the bike.
Happy cycling!