When I was little, I think I assumed my grandparents had always been old. Like they’d been born with white hair and wrinkles. I never pictured them throwing tantrums as kids, hanging around with their friends doing absolutely nothing, or lying awake wondering what the hell they were going to do with their lives.

But they must have, right? They had a whole life before I knew them. Sometimes I wonder whether they still felt like those younger versions of themselves. Whether my grandad looked in the mirror and thought, “Who’s that old bloke?”

Apparently, psychologists have a name for the age you feel inside: “subjective age.” There was a study in Denmark where people over forty felt, on average, about twenty per cent younger than they actually were.

I can see how that happens. You have another birthday, but you don’t suddenly feel a year older. You’re still you. The number changes, but it doesn’t necessarily feel like anything has changed inside.

In Korea, we say “age is just a number”. But we spend a lot of time telling people what they should be doing because of that number. You’re too old for this. You’re too young for that. You should have settled down by now. Come on, act your age.

And the annoying thing is, I’ve started doing it to myself. Inside, I still feel like a young guy. I want to try things. Do something stupid occasionally. Enjoy the hell out of being alive.

Then, almost immediately, I hear myself thinking, “You’re too old for that now. Be sensible. Make money first”

What if I keep putting things off because I’m supposed to be responsible? What if I spend so long acting the age I’m told I am that I never get around to doing the things I still want to do?

Then one day, someone calls out, “Excuse me, sir,” in that careful voice people use with elderly men.