We've all heard and probably have used the saying "time flies," but why does this expression resonate more and more as we get older? From being a happy-go-lucky child counting down the days of school left until the summer holidays to finding ourselves in adulthood with responsibilities like a full-time job and bills to pay, everything changes in what feels like a blink of an eye. While there isn't any scientific evidence that explains why we feel time moves faster as we age, there is a theory that may provide the answer. "One is that when we are older, we tend to have lives that are more structured around routines, and fewer of the big landmark events that we use to demarcate different epochs of the 'time of our lives,'" Cindy Lustig, a professor of psychology at the University of Michigan, told the Daily Mail. She explained how as children we have fewer experiences to reflect on. And so 20 per cent of a five-year-old's life is just one year and in this year there are momentous milestones and life experiences. While the same duration of time only two per cent of a 50-year-old's life who wouldn't have as many new experiences within this period. The professor added how our brains often merge similar days and weeks together and this blending of memories means that many of us can remember something they've done once rather than recalling the hundred times they have done it before. Well, there you go - something to think about whenever we feel old and like time is passing us by. Sign up to our free Indy100 weekly newsletter Have your say in our news democracy. Click the upvote icon at the top of the page to help raise this article through the indy100 rankings.