I JUST bought a 2004 GSXR 600 as my second bike. I had a Ninja 500 last year, and I was shocked at how much more power the GIXXER had. He should probably learn on a little smaller, but if he REALLY wants the GIXXER get frame sliders and leather because he'll probably lay it down. I LOVE the GSXR 600 so much, but I have a little more experience. Its the difference between what you WANT to hear and what you SHOULD hear. He should start smaller is he's never ridden.
I followed exactly the same path, got my licence (French) in 2019 and rode a ninja 500 (EX500D/GPZ500s) for 2 years to get to know what it's like to ride, get accustomed to positions, reflexes and such. That first bike did require repairs (old carbs, old electronics), but that allowed me to work on it and see how bikes work. Plus, since you always drop your first bike, let it be a bike that's not worth too much. Although these bikes aren't too complicated, I would recommend to make sure you have your own garage at home to work on it.
Now to the point, after 2 years spent on this first bike, I have just got myself a 2005 GSXR 600 and I can't describe the pleasure it is to ride such a bike
AFTER you have had time to learn on a beginner's bike. That makes you feel confident about the bike, plus you're aware of all the risks and already know what to do/not to do, predict other drivers' behavior and whatnot.
Here in France, we actually don't have much of a choice : one can't simply get his licence and drive a powerful bike : you must go throw the A2 driver's licence, which basically limits the power of your bike for 2 years, hence no gixxer. Then you get your A licence and you're clear to go choose any bike you want. At first I thought that was lame when I compared to the US system, but in the end it's a good way to go.
Anyone wondering if they should get a gixxer (or such) first or a lower cc/lower power bike first, my advice is get a ninja 500 or CB500 first. You won't believe how much fun you'll have after having spent time learning on these bikes before getting your hands on a sports bike.
Bonne route à vous !