Finding the real me: looking into the past

Time changes everything, and of course, I am not an exception.
Looking at some photos and videos from my childhood, I could not help but feel very sad. To be more precise, I felt a strange feeling of loss.
The 10-year-old me I found hidden in the digital album was confident, energetic, and deeply into books. I liked to be a leader in every group. I didn't hesitate to accept challenges. And I was never bored of anything. Everything in the world seemed to be an interesting subject of observation.
I thought there was nothing in the world that was impossible if I had enough passion and courage. Even though it might sound a bit optimistic, part of it is still so true. Now, I guess time has changed me into a more realistic person. Now I care more about the consequences of what I do, worry about the possibility of failure, and hesitate to think of extraordinary ideas. My expression has changed too, with a somewhat tired, faded light in my eyes.
Is this what "becoming older" means? Does time always slowly take away the fresh, energetic mind a person once had? Do I need to fight against it to keep my spirit alive? I guess I should. 
Maybe I'm just imagining an image of a young and "perfect" me. Maybe I'm ignoring all the positive changes I've been through. Still, to me, the past is something I always need to remember. It is a secret passageway where I can bring pure passion and curiosity from. It is also a part of me that is buried deep inside. I am trying to dig it up now because there's absolutely no reason it should stay hidden in the dark. All I wish is to be who I truly am.