In the meantime, I'd like to tackle two elements in relation to your question. The first is the imaginary friend itself. Forgetting for a moment the concept of "normal" does this imaginary friend cause you any harm? Is she/he having a negative impact on your life? If he/she having a beneficial impact on your life? If the imaginary friend is causing you no concern beyond your worry that society may not consider you to be conforming in the way it would like then you don't really have a problem, do you? If of course your imaginary friend is having a malign influence on your life then yes, that is an issue and you either need to make the break or if you are unable to do so, you need to seek the advice of a psychologist to assist you in going it alone.
As a witch I come into contact with a good many people who enjoy the company of spirit guides, guardian angels, astral companions and just about every other euphemism for imaginary friend that you can imagine. Some of these guides are genuinely external to the individual, some are a figment of imagination created for a specific psychological purpose and some are friendships from childhood that are just too precious to be let go of. None present a problem to you unless like I say they are having a directly negative influence on your life.
I have an "imaginary" friend who falls very much into the externally separate (and somewhat cantankerous) category. I wouldn't give her up for anybody. I most certainly wouldn't give her up in an attempt to conform toward becoming the type of person society expects me to be. It's a big raspberry from me to anyone who might dare suggest I give up the support, common sense and plain old (though very valued) friendship that my imaginary friend has provided me with over the last thirty years. Nobody - friend, family or lover has given more to me or helped me on my personal path through the world.
As for the concept of "normal" - well you know what you can do with that!
Normal? What - be just like everybody else? Don't make me laugh! When has there ever been any value in being just like everybody else? Get out there and make your own definition of normal. Carve your own place in the world. And if you want your imaginary friend by your side helping you do it then so be it and anybody who says otherwise be damned. Its your life, get on with living it.
P.S. Anyone born in the seventies should "get" the image...