Seek out novelty in the mundane
Children have many novel experiences, and time, therefore, seems slower to them, while the routinization of older people’s lives means that time seems to pass at an ever-increasing rate.
You can combat this by cramming more novel experiences into your life.
An alternative is to pay more attention to every moment, however mundane—to find novelty by plunging more deeply into your present life.
Try going on unplanned walks to see where they lead you, taking up drawing or birdwatching, or playing “I Spy” with a child—whatever draws your attention into the moment more fully.