I hate when that happens. I look about 16 to most people, but I'm 25 and it drives me nuts sometimes. I'm not a flashy person, but I do have a taste for high end stuff, so for most people it's not obvious that my handbag/shoes/etc. might have cost me a fortune. I'm not rich by any means, but I save a lot of my money and only spend it on things that will last me a long time.
I could care less what people think because I'd rather have 2-3 great quality items than a closet full of cheap stuff that I get tired of after a while. It doesn't matter if you have to save up a month's worth of pay or just a day's worth, you have just as much right to buy what you want as anyone else.