Keep the mind moving
When we were children, our minds never stopped. We were open to new experiences and absorbed as much of them as possible. We learned fast, because the world around us excited us. When we felt frustrated or upset, we would find some creative way to get what we wanted and quickly forget the problem as something new crossed our path.
The Greek thinker Aristotle thought that life was defined by movement. What does not move is dead. What has speed and mobility has more possibilities, more life. You may think that what you’d like to recapture from your youth is your looks, your physical fitness, your simple pleasures, but what you really need is the fluidity of mind you once possessed.
Whenever you find your thoughts revolving around a particular subject or idea - an obsession, a resentment - force them past it. Distract yourself with something else. Like a child, find something new to be absorbed by, something worthy of concentrated attention. Do not waste time on things you cannot change or influence. Just keep moving.