It's all so interesting to think about! I think the core of what makes us unique is pretty much fully formed by 16. What we learn after this changes or fine-tunes us in little ways here and there.
I love that you had the feeling you could do anything at that young age. I was the quite the opposite, it took me another couple of decades to adopt that I can do anything attitude. It was as though, the instant I adopted that attitude, the entire world opened up. The fears never left but I just became willing to challenge them and at a certain point that just became kind of addictive.
I hope you're enjoying the weekend!
I think that's where the key of it lies. The reason why we either lose this feeling as we go (and get scared) or never fully embrace it. I'm glad you embraced it - one can definitely tell ;)