In watching Simon grow up, it has been fun to watch him start to engage in imaginative play. Sure, it's coming a little later due to his ASD, but it's there, and it's fascinating to watch. I suppose most of your imagination is derivative in your earlier years, but there comes a time when you start to come up with more stuff on your own. Sure, it's always colored by life experience, but the "spark" can still conjure some pretty crazy stuff.
I think it peaks in your late high school or college years. It's a great time of your life because you don't really know constraints. Anything is possible because life hasn't really taught you otherwise. As the years pass, inhibition starts to grow due to failure, social contracts, perception of risk, knowledge of consequences, etc. I suspect your brain continues to imagine things, but we might not notice as much because we quickly cast aside those ideas that pop up as impractical.
Simon gets ideas and wants to try them out, because he doesn't know any better. He sees a box of Duplo, and he wants me to build a bunch of stuff because he doesn't realize there aren't that many blocks, and that they only fit together in limited ways. Even the fact that he can't himself manifest the things he imagines does not deter him. That's fascinating to think about... a child at that age is not deterred by little details like reality.
I hate that we lose that. With the Internet making it possible to reconnect with people after decades, sometimes I'm disappointed when it seems like, well, they settled into a comfortable routine and they're happy. I can't judge, certainly, as I've had more ups and downs than I can count in every aspect of my life. But I wonder if they can even imagine something happier, more awesome or world changing.
Does it matter? It might. I think a lot of people see the world as an awful and dark place. Imagination combined with the will to make something happen is an inspiring force that lifts people up. Whether it's philanthropy, our work, our role as parents or as elected officials, putting aside our constraints and letting our minds run wild can only lead to great things. When it's time to add the constraints back in over the things we imagine, then we're forced to be even more creative and solve problems. The constraints shouldn't make our imagination irrelevant, they should only make it work harder.