I think the title pretty much says it all, not sure what else I can add to that.
I can remember clearly what I wanted when I was about 16 and I know if I had gotten it, I'd probably be disappointed with it by now. It even did have personal meaning, but in 4 years I've changed so much. I have no idea where I'll be ten years from any point in my life. So it's hard to actually account for those kinds of things. I'll be thinking about it for a while before doing anything, but I'd prefer not to be 30 by the time it happensMy best advice that I can give you is wait until you're old enough/mature enough to know what it is you really want. At 17/18 you're going to change so much still that what you like now might not be what you will in even 10 years, and what ever you do make sure that the piece has some personal meaning to you as that will be something you'll always be proud to sport IMO.
It's when you go into a shop and pic something off the wall just because it "looks cool" is when you're almost guaranteed future regret.
just my .02 cent.