Despite the continuos change of our body and mind over time, there is a constant self that threads through our entire life.
It is the same self we were as a boy/girl. We can connect with our young selves in memory; we know we are essentially the same person.
What is that constant essence that remains unchanged?
It is the sensation of pure consciousness.
Witness that sensation, then you will truly know who you are. You will be enlightened to the true nature of self.