I wouldn't say either, to be honest. Lots of girls spend money on makeup and clothes, while some don't. Lots of guys spend money on dates, some remain single. I think it all kinda balances out and depends on the individual, really.
Which ever chooses to spend more money at the time. It's entirely subjective and dependent on an analysis of income, wealth and spending. I could bring up some stats from the census or the bls, but that requires time :P you can do it if you're genuinely curious.
I'm going to say girls. Besides the regular food, rent, phone bills, etc I spend a lot of money on clothing, hair, makeup, and what not. I also spend a sh*t ton of money on concert tickets and traveling to concerts because I'm a music junkie.
The only things the 21 year old guys I know buy beyond normal spending is alcohol and video games.
I think girls and guys spend equally just in different ways. Girls spend money on looking good ex. Clothes,make up, and getting their hair done. Where guys spend money on fixing up their cars,gaming systems,games and other such things
I'm as frugal as it gets. For pete's sake, I take all my showers at the YMCA. The only thing I generally spend any surplus money on is the occasional concert. And hey, I'm 21.
Also, here's an idea, maybe it wouldn't be so expensive for you women if you didn't suffer from the illusion that having more clothers, more make-up, perfect hair and more shoes suddenly makes you more attractive.
Money-wise? Easily a girl at basically any age. Then again, guys do tend to buy expensive electronics and whatnot hmm... still seems to be women with more spending issues. But SocietysBomb is right, girls get free drinks (stop buying them free drinks guys, make them work for it beyond their appearance) and that is costly if you're out drinking a lot. But I'm not soo...