ANDY'S ANSWER: At age 12 you coud easily still have another 4 or 5 inches to grow. Although you can still be growing very slowly until age 18 or 2o, most girls will have reached within an inch of their full height by age 14.
There is a formula that you can use to give you a general idea of how tall you might end up within 2 inches one direction or another. If you are a girl, add your mother's and father's height together and then subtract 5 inches and divide by 2. If you are a boy, add your mother's and father's height together, add another 5 inches and then divide by 2.
If I had to guess, I would say you are going to be just under 5' tall when fully grown.
Below is the recording of Andy answering this question.