As we advance in years, I don't think we change so much as we learn to hide. We filter our thoughts so that only the cleanest and purest escape our lips. We learn what's considered rude, or just simply, what is the done thing, and behave according to social conventions. Why is the cutlery in a kitchen always in the top drawer?
We learn. Learning has been both a blessing and a curse. A blessing, obviously, because it increases our ability to reason and the result is efficiency. Yet a curse, because it takes away innocence. Learning is the acceptance and the ability to adapt to that which we cannot change. When we accept that there are things outside of our control, we change the only thing we can: our behaviour. And when everything has to go through that system, we have lost the quintessential human spirit (or at least, in appearance in the public arena): our childish innocence.
People who have known us since we were born tell us that we've grown up. That we're now so tall, that we look so much like our parents. Of course we've changed physically.
But somewhere inside us are still the traits of children. Those are the things which never change. Think about how the Cold War started. Each country wanted to be the best, so in the most simplistic, childish manner, they embarked on a mission to outdo each other. Now, we look back and wonder how they could have been so primal. But if you were in their shoes, what else was there to do?