Vladimir, I mean no disrespect, however, I believe what you're feeling is similar to having a crush on someone. Stick with being best friends for now. Get to know her better. Do you have the same interests, like the same books / movies / hobbies? Examine your feelings for her carefully. What is it about her that makes you feel as if you love her? If you've known her for several years, as you have indicated, keeping your feelings to yourself right now won't make any difference.
You might ask her, "Do you think kids our age can be in love with someone or do you think we are too young to know what that means?"
If she asks you why you are asking this, you might just tell her that you had been thinking about this and just wanted to know what she thought.
You are going to be attracted to many girls in your life, Vladimir. So be careful in revealing your heart too soon; no one likes to get hurt. Examine your feelings and find out what it is that is attracting you to her. I'm not saying that you should never share your feelings with someone. I want you to be able to handle rejection when you do get rejected by someone. It will happen - it happens with everyone. Hope this helps. Good luck.