(This appeared in Newsday’s Act2 section)

Looking in the mirror doesn’t shock me. I don’t appear a bit older than yesterday. But coming across the numbers in a check register from my college days, unearthed among a stack of old papers and photos, produced quite a jolt.

Look: A check for a month’s rent for an off-campus room, $36.56. For a pair of slacks, $5.13. Lunch at the local smorgasbord restaurant, $1.37. A year’s university tuition and fees, $445. Talk about old.

This is the kind of conclusive evidence — more specific than carbon dating; better than counting the rings in a tree trunk or checking a building’s cornerstone — that will zero right in on the age-old old-age question. That, and a related query: When was the last time anyone wrote checks for these items?

I read where it’s possible to calculate the age of cattle or horses by examining their teeth. And it can be concluded a dog is old by noting that it “lays around a lot.” Hmm. More precisely: When you hear a cicada rattling, you can be sure it just turned 17.

But regarding us humans, if you were one of those carnival workers who charge customers $5 to guess their age, just on sight, guided only by evaluating wrinkles, saggy skin, lack of hair color and so forth, I’d argue you are practicing art, not science. (Or something closer to a scam than a scheme.)

Let’s say the subject in question wouldn’t let you get close enough for the pinch test. (Pinch the skin on the back of his or her hand to see how long before the skin snaps back. One to two seconds, she’s under 30. Five to nine seconds, he’s between 45 and 50. Anywhere from 35 to 55 seconds, you’re looking at a septuagenarian.)

All right, then, first names could offer a hint. If I were a Noah or a Liam, I likely would have been born around 2010, not yet a teenager — just as a woman christened Madison would likely be near a 21st birthday. Michael of Mary? Hitting 70 years old. Christopher or Jessica? Thirty-something.

But those of us with a common handle like John could be from such recent vintage as the 1960s or from as far back 1920s (and going out of style long before our name has). A more specific age figure might be conjured via a culture quiz, determining one’s awareness that Drake isn’t necessarily a university in Des Moines, Iowa, and The Weeknd doesn’t refer to Saturdays and Sundays.

Still, there is a lot of guesswork involved in this matter. I’ve known people in their 90s who still had all their marbles and others well past 80 who hadn’t lost anything off their figurative fastball. Hard to pinpoint their time among us. I thought I had found a formula on the Internet (yes, I’ve heard of the Internet!) that would eliminate the gray area in assessing graybeards’ total trips around the sun, a method to identify the museum candidates.

Except the sixth of the seven steps (see below) is dependent on already knowing one’s birthdate, so what’s the challenge there?

1) Pick the number of times a week (more than zero, less than 10) you would like to go out to eat; 2) Multiply by two; 3) Add five; 4) Multiply by 50; 5) If you already have had your birthday this year, add 1,757. (If not, add 1,756.); 6) Subtract the four-digit year you were born; 7) Of the remaining three-digit number, the last two digits give your age.

Bogus, no? And after running through all that convoluted math, I was informed that I am 60, which I confess is off by more than a decade.

So, back to my old check register, unsettling as its information is, for the facts. There was a check for 11.1 gallons of gas for my car: $4. For tennis shoes: $10.05. For a winter coat: $25.75.

All sobering proof that time has marched on. (Which isn’t all bad.) And no pinch test necessary.