We were at one of those buttoned-up business luncheons — the kind with tablecloths and butter in little balls — when I noticed it.

My first liver spot. Right there, on the hand I was using to stab a cherry tomato as juicy as a marble, was proof positive that I myself was a darn sight riper than the garnish on my salad.

Ironically, my pal and I had been laughing about how we wavered while dressing for this august event. Cher and I are both well past the point of being constrained by our old dress-for-success uniforms. She’d settled on her favorite jeans; I pulled leggings out of the closet. We were debating, amidst girlish guffaws: Were our get-ups age-appropriate?

She’d just reminded me, “You’re only as old as you feel.”

Next thing I knew, I was staring at my elderly mother’s hand fiddling with that salad fork.

The trouble with sage advice like Cher’s is rather clear. How old I feel varies from day to day and sometimes hour to hour. It rattles back and forth between 17 and approximately 90.

I’m far younger, it seems, on sunny days, when I lunch with friends, and right after I’ve met a looming deadline. Older? When I lose my trifocals. When I pull out Pillsbury pie crusts because rolling it out is too much bother. When I hesitate to get down on the floor with the World’s Greatest Grandchild, knowing all too well how I’ll struggle to get back up.

When I got home, I googled “liver spots.” I hoped, somehow, to find good news. No luck. Wikipedia put me in my place, offering the encouraging synonym “senile freckles.” Mayo Clinic’s website suggested creaming them with dubious potions, zapping them with lasers, freezing them, abrading them, peeling them away with chemicals — basically every nasty thing you can imagine just short of cutting off the whole hand.

Or not. When you still think of yourself in unguarded moments as a flower child only slightly gone to seed, confronting signs of age … oh, let’s call it “maturity” … can be both humbling and hilarious.

They sneak up and pounce when you’re not paying attention, like when you’re filling out a survey and checking the age category “and over.” Or while watching the few remaining network TV shows that don’t disgust you — and noticing every ad seems to tout irritable bowel meds, Cialis or toilet tissue.

Do you think getting your first letter from AARP is shocking at 50? Try the moment when the thoughtful waiter automatically figures your senior-citizen discount into the check. I notice, too, that servers have started to address me as “dear” or “sweetie.” They apparently assume that I’m too toothless to bite them.

But I take advantage, too. I no longer suffer in silence when my order’s not quite right. I shamelessly ask for doggie bags. I go ahead and order the pie … right out where other humans can watch me eat it.

Eating out, in fact, is a great time to meditate on mortality. Russ and I seem to be dining earlier every night. That’s led to the advent of the new mealtime that we call (in the spirit of midmorning’s brunch) “lunpper,” or maybe “dinch.” It’s when you consume the final meal of the day while the sun is still up, even in January. Partly, this occurs because IHOP offers two-for-one entrees to well-aged patrons from 2 until 5 p.m. There’s another benefit, too. When we wrap it up well in advance of sunset, our Rolaids last much longer.

When it comes to advancing age, mark me down as mostly enthusiastic. For one thing, it’s much better than the alternative. For another, it has given me a giddy sense of relief from so many everyday “thou shalt nots.”

Once a typically reticent Norwegian, I now brazenly talk to strangers wherever I go. It’s lots of fun — especially when a cheery “hi there” startles young iPhone addicts so greatly that they stumble over their own feet.

I don’t worry nearly as much about making mistakes. I’ve learned that the people around me are paying far less attention that I ever could have imagined. Just dust yourself off, patch the damage and — if anyone bothers to ask — assert, “I meant to do that.”

Fashion faux pas? Forget ’em. As I draw near to some indeterminate point of no return, my mother’s ageless wisdom has begun to sound less like a lament and more like a blessing: Nobody really looks at old ladies.

Even my own advice seems to be getting better and better … or, at least, younger mortals are less likely to argue with me. I grin from ear to ear when I catch our daughter sharing Mom’s Greatest Hits with her own peers: “It’s not all about you.” “You’re just a bit player in someone else’s movie.” “Not your monkeys — not your circus.”

And by now, I’ve lived long enough to hear the four most beautiful words in the English language: “Mom, you were right.”

As for that little liver spot, I figure it’s clearly premature. In the meantime, I’ve plotted out a way to cope if it invites more friends to the party. After weighing removal by scouring, freezing or chemical peels, I’ve settled on a simpler course of action. I’m looking for a single, sequined glove … or I’ll tuck my hand into a pocket for the duration.