Do you think age defines all? There's wording in Tamil "Sathikka vayathillai" to achieve, age is not a barrier, and the same goes with anything as you can't decide what your heart desires despite the health condition and age. Though I know fatigue is not only for the body but for the mind as well. But many a time, the body could not cooperate with the energetic mind or interest level; it is perhaps because of weakness or illness, not age.
Age, in general, is considered to be a part of the time or phase that takes place in the body and mind as well, but what we have done is define things that have to be done at specific age only. I'm not going to deny that because things generally work adjutant with that, and true to an extent. But this is not with all the cases - some exceptions have the right to think out of the box. It is possible or not is up to the one who tries, and we should not deny it generally because of age.
Like the time that does not wait for anyone, age keeps rising every year either you consider it or not; our body keeps worn out as we used to it, our mind may also feel tired, but we can't say it is the state of mind with everyone. I see many young people feeling lazy and lacking interest/energy to do things; at the same time, I see brisk elders walking thousands of steps daily, working hard, and reading a lot to keep them at a steady pace even though they can't work beyond a limit. What I see is the way they try and experience life despite their age.
Is there anything that only kids should enjoy these things and adult these and olds that? You can't refine or define your mind as it is beyond your reach, and it consists of many other things than age. Someone in mid-age who loves to wet in the rain would hesitate to step out of the home thinking what the society would say? Of course, are you a kid to play in the rain? Is rain belong to kids? If you are good enough with resistance power (desire sees that?) or ready to face the illness that follows, go ahead and enjoy the natural showering.
I would say kick away the age barriers. I hear many opposing it and have reasons to argue, like is it ok for kids to explore adult things? Those who turned age 18 considered adults because 18 is a general age or stage where individuality happens. But is it questionable whether everyone over the age of 18 is mature enough to handle their uniqueness? I have seen people below the age of 18 being responsible and acting consciously and those aged to behave ridiculously.
Some hesitate to treat the child hidden within them, thinking about society and stuffing themself in a stressful mood, and act as if they lost interest in the childish things. How many adults play video games on the smartphone, and isn't that kids' stuff? lol
I'm not complaining but want to encourage you to explore things that were fair, lawful, and harmless to the circumstances - that society put behind the bars of age. If someone feels young at the age of 60, let it be, and age is only a number, and it counts only on aging and never reads a mind. Our life is surrounded by a lot of little happiness, and we should not miss those just because it is not related to our age.