Stop. Just stop. It is trite, self-indulgent, and pointless. It has nothing to do with accepting who are. If you're writing about how it will get better, then it is pointless. Even if you could even contact your younger self, the letter would irrevocably alter the perception of what is to come and thus change where you are now. If you are writing to warn that your younger self shouldn't do this or apologize for you own stupidity, then you already know what you need to do and stop indulging in self-pity, get off your duff and do something about it. By placing the blame in your past, you have officially denied responsibility in the present.
Look. You cannot time travel. You made choices. Some are good, and some are bad. Things that have happened cannot be undone. Writing to your self is the worst form of self aggrandizement, especially if you are a celebrity. If you must, write a "tell all" autobiography or even a "tell some" autobiography. Since, however, you cannot contact your younger self, that means you are writing for what? Who? Me? I am not interested in your self-postulating and inner search, even if you hired a really good writer to polish your tripe.
If you are trying to find yourself, I have a suggestion. Look at the spot where you last left yourself and get over it. Time to move on and quit wallowing in your own ego and inability to come up with something creative. Dear younger self: it may or may not get better. Expect ups and downs. If bad stuff happens, get over it and move on. If some good stuff happens, count yourself lucky and move on.
IN OTHER WORDS
GET OVER YOURSELF AND MOVE AHEAD. THERE IS NO GOING BACK.
*And yes given what I just wrote, I realize the irony of using a banner from a site dedicated to these trite and silly letters.