To Whom it May Concern;
Even though you cannot find any foundation in the real world, you need to realize that your siblings even if they consider you as an annoying spoiled brat... you are the constant thing in their life that they never think will change. Perhaps it is good to stick with what identity they assume of you so long as it does not conflict with your "growing up."
Your older siblings can trust you to always be you. That trust is love. They can share all of their secrets with you. They can disclose information to you that they may not even tell their best friends. There is a responsibility and honor to be this person.
Your parents rely on the fact that you are a helpless creature. Sure you can milk them for all they are worth while you talk to them, but when you are on your own. Out of sight and out of mind. Then is the time to practice those things which make up your growing independent personality.
Never burn the bridges behind you. You may slip back into that "baby of the family" role when you are around people who knew you then, but family is important. They will not turn their backs on you when something bad happens. And let me tell, you on this journey there will be plenty of bad stuff that happens. So be that anchor that your family needs. And they will supply a ready foundation for you too.