My 70-year-old father tells me he’s routinely startled simply by seeing his face in the mirror. “Who’s that old guy?” he thinks. Science shows he’s far from alone in this feeling.

Neuroscientists have explored the puzzling gap between our real age and how old we feel in our heads (aka our “subjective” age) and discovered that, on average, middle-aged adults in Western societies feel 20 percent younger than their actual number of years.

How old do you feel? 

It may be clear that most adults feel younger than they are. Why remains a bit of a mystery.

One theory is that years rich in new experiences seem to make more of an impression on our brains. When we enter into maturity, we settle down and the years seem to count less, throwing off our internal clocks. 

“Adolescence and emerging adulthood are times dense with firsts (first kiss, first time having sex, first love, first foray into the world without your parents’ watchful gaze); they are also times when our brains, for a variety of neuro­developmental reasons, are inclined to feel things more intensely, especially the devil’s buzz of a good, foolhardy risk.”

 Several people suggested their subjective age was frozen at a particular point because of a trauma they experienced, like the death of a loved one. A few “old souls” told her they felt older than their years. Meanwhile, cross-cultural studies show that people in societies that revere elders seem not to internally discount their years as much.

Can you change your subjective age?

There may be some broad patterns in how people settle on an internal age, but the process is clearly quirky and personal. If you’re feeling aged beyond your years by the stresses of being an adult, are there ways to feel internally younger? 

Yup, answers science. Here are the steps research suggests — and they are pretty simple, if not entirely easy.

The first is just to sleep more. A new study found that simply getting enough rest for a month made subjects feel, on average, nearly six years younger.

Traits like curiosity and openness to new experiences that are associated with youth are also associated with slower physical aging. When you think like a kid, your body seems to stay more youthful for longer. So if you want to be more open and curious, signing up for new activities or exploring new places will likely move you at least a little in that direction. 

As a side effect, they may also make you feel younger. And even if you don’t, research shows that fresh experiences today lead to more happiness tomorrow and slow the signs of physical brain aging.