Im just wondering my 15 year old brother is really skinny and he wants to gain weight but cant please help me how do i help him put on weight?

Check for thyroid: Young people grow at different rates. This could be a skinny stage of your brother's growth. This being skinny may be a genetic trait. If either of these findings are the cause your brother should eat a well balanced high calorie diet with the help of a dietician. Before making this assumption he should see his MD and be sure he does not have a med. problem like a too active thyroid.