Please don't do keratin at your age if you mean the kind with formaldehyde in it. Many of the brands out there have come out with "light" versions that claim to be formaldehyde-free. My advice is to use one of those. They probably won't work as well as the original formulas (because in my opinion, it's the formaldehyde that makes these treatments work), but at 12 years old, please don't expose yourself to a carcinogen like formaldehyde.
Also, do you realize that keratin is $200-$400?
Also, depending on what your hair looks like now and how strong of a formula you intend to use, your hair could see dramatic changes.... please do your research before taking the dive!