It sucks that the notion of "play" -- as in free-associating, undirected and creative/lateral activity -- sort of disappears as an adult. Perhaps it also contributes to a loss of neuroplasticity, weakening of lateral thinking, and other cognitive changes.
I'd love to be able to reclaim the notion of play, but I honestly don't know how. Why do we look down on (adults doing) it? Are we so captivated by purpose, structure, and certainty that we fear anything outside of that framework, or view it as social deviancy? Is it the association with childhood and immaturity? Are there differences along Western and Eastern modes of thought?
But counterargument: Adults play, just in more "advanced" ways. We've exhausted the top-level stuff in breadth, and now we play with deeper things, which means hobbies, sports.
I agree on some level, but I still think that there's something lacking even as we do pick up hobbies. In following hobbies, we are still purposeful. We still constrain our own state spaces, and direct our activities, coloring them with some form of purpose or ruleset.
Play and Risk Management
Perhaps it's the adult responsibilities, the singular notion of survival and reproduction that naturally constrains us. Therefore, we must adopt a purpose-oriented, proof-seeking, constrained-space mindset.
The exercise is to get out of that mindset for at least some time. It seems difficult for adults. I'd imagine that for particularly conscientious people it is more difficult. I think order arises out of risk management, as order and structure induce proof and certainty. i believe it can be mathematically modeled as an optimal strategy. So this conscientious attitude likely is a defense against scarcity. It would explain the conscientiousness paradox. On the flip side, abundance and lack of scarcity gives us room to optimize and explore, and break more constraints.
Play and Mindfulness
It's well known that there's a link between meditation and neuroplasticity. An element of mindfulness is a sort of "emptying" of thoughts. From another perspective, this is analogous to removing constraints, and expanding the space of possibilities (state space of mind-states?). A core function of play is some degree of detachment from purpose. Meditation explores this concept to the end in its concept of "emptying".
Play and Art
Art is expression, and expression requires some degree of expression. There are, of course, self-imposed constraints when it comes to art, since there is often a message that requires conveyance. But the key that connects play and art is the degree of freedom allowed within both. Play can be seen as a form of art with the purpose of expressing joy, and art can be seen as a constrained form of message-passing play.