Well, it's your money. I didn't see your age, actually. I guess that means it will be okay as far as the actual system, because your parents will pay the bills and let you save up your money indefinitely.
Still, the Xbox doesn't have as many E-rated games. I've heard that a lot of the best games for it are rated T or higher, so the games you want might end up being too adult for you. The other problem is that Xbox is better as an online gaming console than a standalone gaming console.
In other words, you'd need an Xbox LIVE subscription in order to get the most out of it. That's about $8.00 a month.
I mean, think about it logically. There's the initial investment in the console, a subscription to Xbox LIVE, and then shelling out for the games. One of those is a recurring expense. EVEN assuming you can mow enough lawns and get your allowance high enough to pay for that, how are you going to convince your parents that you're old enough for online gaming, or for those T-rated games?
We've established that you want to get it. Now, all you need to do is figure out how you're going to do it. Good luck.