When do I need to get a business license for photography?

I'm 17 and have been taking photos for a couple of years now. I have had my work in art shows, and am taking senior pictures this upcoming month, so I'm not a total newbie at this. I have invested in a nice D3000 Nikon, two tripods, and two lenses. I've been holding off on selling my nature and portrait photography, because I can't seem to figure out when I need to register as a business. Do I do it when I'm 18, is there a certain amount of money I can take without needing to register? Any help is appreciated.

No, you do not have to be 18 to get a business license. You simply go to the finance department of the city or county where you business is domiciled (like your home) and get the license. The fee is usually a small base fee with an additional amount based on sales volume. However, with what you doing now I would not get a license. When you are doing it full-time, that's another story.