recalling yesterday on your 18th birthday

As an adult, you can never really recapture or re-member how you thought as a child, because your view of it will always be through the lens of adulthood. It's like trying to remember what it was like to see written words before you could read - what it's like to look at writing with incomprehension. 

On the one hand, it wouldn't mean anything. It would be like looking at trees or rocks or whatever. It's only an adult (and one who can read) who can have the thought - I wonder what it would be like to look at words without understanding them. So, it's an adult thought and you are already defeated. 

On the other hand, it doesn't matter. The same principle applies to any two points in your life, so don't worry. There are things that you don't even see now that will be revealed later - amazing things.