How much time do you spend playing? Really playing, not just going through the motions. Not in a passive mode, such as watching television or going to the movies, but active, participatory play. Probably not as much as you should.
Do you feel guilty when you do manage to find some time for play? Unless you are rather unusual I suspect you do have some guilt feelings, even if they are hidden below the surface. There are so many things you know you should be doing, so why are you wasting time playing instead of getting them done? Is that a familiar question? Even if you don't ask that question of yourself, probably someone close to you does - your partner, a parent, etc.
Most children play a lot, of course. Why do they play? You could answer "because they enjoy playing", which is true. But why do they enjoy playing? Because evolution has set them up to enjoy it. Play has an important purpose. It is a key element in their learning curve. Learning not only about things in the outside world, not only about relationships and ways to nurture them, both of which are very important, but also about their own capabilities and how to stretch and grow those capabilities. Learning how to improve their problem-solving abilities. Learning to expand their imagination and creativity.
Think about this for a moment. Why should you decide there is nothing more for you to learn? Why decide that you are so perfect at creating and nurturing relationships that you don't need to learn how to do so even more powerfully and effectively? Can you really say that you have fully explored all your own latent skills and abilities and have developed them to the point where there is nothing you can do to improve them? Are you as creative and imaginative as you could ever be? Unless you can really say all this, you still have the need to play!
Even if you ignore all those practical benefits of play, it has other important functions too - one of which is to give us laughter and happiness. Do you laugh as much as you could and should? Are you as happy as you could be? Assuming you laugh a lot and are happy most of the time, is there a good reason you should not laugh even more and be even happier? I cannot think of one good reason not to laugh and be happy, but know of plenty of reasons to laugh more and be happier. One reason is that being happy and laughing is a state I enjoy far more than any alternative state. If I have a choice between an enjoyable state and on that is less enjoyable, why would I choose the less enjoyable one? Another reason is that people who laugh and are happy have far less stress in their lives. As a result, they typically live longer. A double benefit - you can have a longer life, less stress, and be happier in all that additional time the happiness and laughter has bought you.
Now that (if I have done my job properly) you recognize the value of play, you can use this to squash that little voice inside that tries to tell you that you are wasting time, being silly, reverting to childhood, or anything else it can say to make you feel guilty and stop playing or stop enjoying the play.
Decide now that you are going to spend more time playing. Where will you find the time to do this? Take a look at all the things you do each day that are not essential but also are not play. I am sure you will find plenty. Simply use some of that time to play instead, and start creating a more fulfilled, happier life more filled with laughter and enjoyment.