I am thirteen and you have got a thin line going across your forehead Is this just form growing and is there anything that can be done to get rid of the line?

This lines appearing on your forehead, means that you are getting older. Thus, it is also a sign that you toiled the whole day under the heat of the sun. Moreover, those lines growing because of the problems in life that you are facing right now. Frowning, causes these lines to appear too.