$600 on clothes when you're 15? Clearly this kid comes from a ridiculously rich family but when I was that age (all those [5] years ago) I'd spend it on something a lot more usefull like a guitar
or ... damn, I can't actually think what I'd do with so much cash at that age.
Seriously even with a fake he couldn't go clubbing looking so young, and where else are you going to wear top-line desinger? Otherwise if it's just a vanilla dress shirt, when you're 15 and not trying to impress top execs it won't matter if it's a discounted Alfani at Macy's (and btw their fitted shirts are pretty damn good for $30) or a $300 Versace.
It is possible, however, to get plenty of designer clothes for a budget like that if you have patience and will. I definetley don't spend more than $600 on clothes a year - but nearly everything I buy is desinger. You have to do two things - shop at the big sales in the right stores (and of course eBay from reputable sellers) and also be on the lookout for new small designers that will often have great pieces for prices that are quite a bit below the top-line runway stuff. For example get gsus instead of dsquared.
Speaking of top young men's labels, btw. Here are some I like in no particular order:
J.Lindeberg, Diesel Stylelab, Guess by Marciano, Gsus, Dsquared,
troVata(*plug*
), Fake London, Evisu, Maurice Malone, Ringspun, Da Nang, 10 Deep, Aem'kei.