Recession of gums is most commonly caused by deposits of Calculus On The Teeth which cannot be removed by tooth brushing and require professional cleaning by the dentist through a procedure called as scaling. This should be followed by guidance about a proper brushing technique so that you can maintain the results in the future because gum recession is more or less and Irreversible damage unless treated by Different techniques like gum surgeries. Please search for a dentist in your vicinity using Practo and try to schedule an appointment as soon as possible before further damage occurs. You are too young to be experiencing gum recession. Regards.