Good morning ! I don’t know anything about you because you don’t even mention your first name. But I am happy to answer your question, because it is important.
First, you need to know that the word “depression” is a word to be very careful with. First, because it is used (too) often to qualify very different things. And especially because it gives the idea that “depression” is an illness (like the flu or measles), which does not help to get out of it.
So I do not know if one can, at 12, be “in depression”. But I know that you can, at 12, be very unhappy, or unhappy. And, in general, for two kinds of reasons. Some, of which we are aware: problems with others (family, friends) for example, or with oneself (his reactions, his physique). But others, too, of which we are not aware. Because there can be, in our lives, whatever our age, things that, without realizing it, we do not support. And you have to be able to identify them.
It is therefore very important, when you are not well, not to be alone. And to find someone with whom to discuss what we know is wrong (to see how this could evolve); and look for what, without being spotted, would go wrong. It would therefore be useful for you to think about the person who (in your family, your entourage) could help you to do so. Knowing that you can, also, if it seems necessary to you, ask for the help of a shrink. The social worker at your college will certainly be able to tell you where to go to find one.