How dangerous would it be to start off on a 600cc sport bike?

I want to buy a sport bike when I turn 18 (in a few months). I'm 5'9", 140 lbs, so I'm not large by any means. I'm thinking of getting either a Gixxer 600 or a Ninja ZX-6R.

Someone told me that the new Ninja 250r would be my best bet, considering I've never ridden a motorcycle of any kind before. He is the kind of guy who knows what he's talking about since he owns a gixxer 750, and he is also the main mechanic at only 20 years of age at the nearest bike shop in my region.

BUT, he also mentioned that a 250 is going to seem slow after the first month and that I'll be wishing I'd gotten a 600. He also said that if I started out with a 600 I'd probably "rape" myself on it, and if I started on a 1000 I would definitely "murder" myself in the first week.

So, I guess my question is, is it really that dangerous, or was he just trying to watch out for his own back in case I did buy a 600 and wreck it (basically so my parents wouldn't get on his rear for recommending it to me).

What would you suggest?

I'm in America, not England, buddy.

My favorite analogy:

Say you want to learn how to juggle. You know nothing about how to do it other than it involves keeping more than two things in the air at a time. But it looks simple enough, and instead of starting with bean bags or tennis balls like people recommend, you decide that juggling knives (600cc) or chainsaws (1000) sounds like more fun. Besides, EVERYONE knows that after juggling three bean bags the only thing to do is move on to something sharp!

People tell you that after 3 bags, you move on to four, five and so on until your SKILL is sufficient to try something more dangerous. Basically, if you get bored with bean bags it's not a problem with the bags, it's that you aren't skilled enough to handle more of them and think that the next logical step is something that will injure you for a small mistake.

Now, if you went for juggling chainsaws, remember that no matter how mature you are, how careful you are, how slow you promise to go and how easy it looks, you are still juggling chainsaws, and the smallest mistake is very likely to permanently injure you.

Get it?

I'd look for a used SV650 or a GS500 if I were you. It's your first bike, not your last, right?

Start on the Ninja. You will never be satisfied with the 250. You have to learn sometime. Just take it easy for a while. Don't go crazy. It will take you a long time to get tired of the 600. They have better resale value also. When you want to try a 750 or a 1000 you will already be one step ahead.

well im 15 and ride a ducati 999r but wouldnt sggest that for you since you havent been rding so long. I would g with the 250r because its not too fast and the clutch isnt as like "poppy" if you know what im saying. Just be careful and use the bike right and you be able to ride anything literally!

Go take a riding course
It will teach you what you need to know to ride.
If you have no experience riding I would start out small and then go for the 600. Crashing a smaller bike is easy to fix, but the bigger the bike the bigger expanse

Start with 250 get a used one for cheep ride it for a year then graduate to a bigger bike you will save yourself a world of hurt.

Buy the bike you want the first go around unless your made of money. Just don't ride beond your abilities and meet your maker.

Very dangerous

Suzuki sv 650 is your answer my friend.
of Suzuki gs500

Well the reccommened engine size is 125cc... I think it would be pretty risky to start high

do not start at 600cc.. start around 75 to 200 at the max..

Get 250cc

law in britan cant start rideing 600 till 21 is 125 till then

Like many more fortunate riders, I learned on minibikes when I was a child. But there were several years gap before I started riding streetbikes. I'm further fortunate that I reentered street bikes on a 250cc.

That said, a 600cc sport bike is definitely harder to learn on than a 250cc with a low seat height, such as a cruiser. I'm also a big opponent against a steering damper on a learning bike... ala GSXR. Low speed handling is very muddled and complex with a steering damper.
Nowadays, 600s are so small, light, and refined, that it wouldn't be that big a deal, if you take your time to learn properly. It isn't like the difference between driving a Ferrari Enzo vs a Pinto.. It's like a Mercedes vs a Pinto. (Should you buy a brand new Mercedes for your first car? If you have enough money, I guess so!) Just really be wary to stay away from the top half of the rev range while learning. Also, be warned that you'll wish you learned about falling on a smaller bike, cuz the damage would be cheaper. You'll eventually wash out the front tire on accident in gravel or the rain, and you might as well learn that lesson on a 250.

Look into insurance first. You are under 25 and male. Insurance on a sport bike will be shockingly high.
Reason being is so many in your age group riding high power, high speed sport bikes with little to no experience crash early and often. It is not the cost of repairing the bike, it is the cost of repairing the rider. The most an insurance company is on the hook for with a motorcycle accident is the cost of the machine, less deductible. Hospital costs to repair the damage the rider causes can be in the hundreds of thousands of dollars.
Stay away from sport bikes for a while until you get some experience. I have suggested in the past a Suzuki DL-650 V-Strom. More comfortable riding position, great on the highway, comes equipped with a real windshield, and has available saddle bags and trunk. Great machine for traveling, yet nimble for the twisties. Bulletproof v-twin engine with fuel injection. Bike is available with ABS. That alone makes it a good beginners bike.
I know I will continue to get thumb's downs for my position.
Tough.
I am talking from many years and many miles of road riding and driving, all accident free.