Date: __ /__ / ____ (Date)
Dear __________ (Name),
I hope this letter finds you in good health. I am really good here. I hope everything is fine with you.
I am writing this letter to you because I am about to advise you about something really important. This might sound silly to you because you are a teenager and you might not see this as very important. But you must understand that this step is really important in life building and if you take this step very seriously, this will help you in building your paths for a long time.
I understand your need to make friends and to have a fun life but make sure you understand what is right and wrong. You must also know how to choose between the right company and a bad company. Always remember this, the bad company might give you a name, fame, and even independence but all the pleasures will be temporary. At the same time, the bad company will even lead you to deep holes and pits of life, from where you will never be able to come out. You might have to pay a huge cost for the same.
So, being an elder brother/sister, it is my absolute duty to guide you. I am always here, near you to clear and discuss whatever you need to know. But please, always think twice before choosing a bad company, and most importantly avoid them as much as you can. You have to go a long way in order to achieve your dreams but keep in mind how are you going to choose your paths.
Rest, you are smart and intelligent. You yourself know how to choose people. Take care and all the best for your future.
Yours _________ (Loving/Truly),