Some say that when people retire, they become invisible to those under 25, particularly teenagers. This often seems true. Several young people who still manage to see me are uncomfortable in my presence, perhaps assuming we have nothing in common, or what I say will be another verse of the annoying "When I Was Your Age."

My invisibility comes and goes, depending on circumstances and who's in my vicinity.

Recently I spotted someone who should have been invisible, and two weeks later experienced something that made me wish I hadn't been seen.

First, an explanation. I am 79 years old, and a few inches taller than most men. I’m told my height — 6 feet 4 inches — can be intimidating ... to people who see me. Mostly, I’m old ... though I like to think I look younger than my years. However, even if I look 69, that’s ancient to a teenager. People in their 20s and early 30s, also may think I'm one of the living dead.

I RETIRED to Bluffton, S.C., where it’s hellishly hot from May until October. Most people here wear shorts, including many who shouldn’t.

Which gets me to the first incident. My wife and I were having lunch at a very nice Bluffton restaurant, when we noticed another customer, a man probably in his 60s, dressed in shorts only a couple of inches longer than Jockey briefs. He might as well have been wearing Depends.

It was an unforgettable, appetite-destroying sight. Spared were younger restaurant patrons to whom this man was, of course, invisible.

Digression #1: When we moved here 15 years ago, I wore Bermuda shorts when I was outdoors. (Not indoors, because my wife and I set our air conditioning at sub-freezing, which is why I have a large collection of sweatshirts.)

All it took was one summer in Bluffton for me to switch to long pants outdoors, because shorts made my legs more inviting targets for the zillion blood-sucking insects that reside in the South Carolina low country.

Now, when I’m out among those who walk around in often outlandish shorts, I feel I should race toward them, shouting like Kevin McCarthy in “Invasion of the Body Snatchers.” My shouts wouldn’t be about pod people, but chiggers and mosquitoes:

“Look, you fools! You're in danger! Can't you see? They're after you! They're after all of us! Our wives, our children, everyone! They're here already! YOU'RE NEXT!”

TWO WEEKS after seeing the man in the too-short shorts, I went to the supermarket, and began my visit in the corral just inside the entrance to fetch a shopping cart. Blocking my way was a young woman, her young son, and an empty shopping cart I initially assumed the woman had returned to the corral, an unusual and considerate gesture. (Most shoppers abandon their carts in the parking lot.)

Then it occurred to me the woman might not have done her shopping yet, so I decided to wait until she and her son indicated whether they were coming or going.

I didn’t take a good look at the boy, but he could have been as young as three, or as old as six. I could tell he was restless, normal for a young boy enlisted to accompany his mother at a supermarket.

His mother had her back to me, and was fiddling with something, perhaps an item that had fallen from the bag she removed from the cart, or maybe she was digging car keys out of her purse, though I could see neither bag nor purse.

When it was apparent the woman and her son were about to leave the store, I deemed it safe to take the one cart within my reach.

THAT WAS my rationalization for lingering. Yes, I could have gotten to other carts easily enough, I suppose, and if, in so doing, I disturbed the woman, I would simply have said, "Excuse me."

The real reason I lingered is the woman was wearing very short shorts, and had — no exaggeration — the most attractive legs I’ve ever seen. (I may be 79, but I'm not dead.)

Digression #2: Okay, you caught me. Obviously I am exaggerating. So let me rephrase: This woman had the most attractive legs I've ever seen in the Low Country, and probably the most attractive legs I've ever seen in any supermarket. She certainly was an antidote for the ill effects of my restaurant experience. (And for those of you who've ever been to this part of the country, yes, I'm aware it's often spelled as one word — Lowcountry.)

I was thankful she was looking somewhere else while I stared at her legs. Years ago, her outfit would have been inappropriate in most public places, but these days anything goes. If you want proof, visit an airport. Or a certain Bluffton restaurant. (I'm kidding. That man I mentioned was the only fashion eyesore I've seen in this particular establishment in more than 100 visits.)

When the woman in shorts turned around, in response to her son’s whining, she saw me. At that point my eyes were on her face, and I gave her my version of an experienced parent’s “been there, done that” smile, but her response was a “why are you looking at me?” glare.

Where was my cloak of invisibility when I needed it?

I didn’t speak; I merely grabbed the cart and walked away. She and her son left, and, I confess, I paused to take a final look at her legs as she led the boy to their car. Luckily, she didn’t turn around and catch me in the act.

YET I WAS PERPLEXED by her glare. After all, she never saw me looking at her legs, unless she has eyes in the back of her head. I believed she should have regarded my smile as a friendly, neighborly gesture.

As I thought about it later, however, I came up with possible explanations for her reaction, which was either annoyance or horror.

For starters, all I had to do was look in the mirror. (Fortunately, even at my age, I can still see my reflection.)

The woman probably was unaware of my presence until she turned around — my wife often accuses me of sneaking up on her; she calls me “The Stealth” — and perhaps the woman was startled to see a large old man grinning at her from six feet away, and thought I had wandered away from my caretaker and expected her to take me home.

Maybe I caught her at a bad time. It's possible she had been digging in her purse, and briefly thought she had lost her keys. Maybe she was agitated by something else, or was aware of my presence the whole time and wondered, "Why is that old geezer still here?"

I wondered if I should have mentioned I was merely having a flashback to when I was between marriages, and had joint custody of two young children who occasionally accompanied me to the supermarket. My smile was a reflex reaction to her son’s restlessness. I thought parents of restless children appreciated supportive smiles. I was trying to show empathy to a woman who didn't need any, not from an aged hulk.

Digression #3: I am so glad those years of having young children are behind me. We had several disputes in the aisles of supermarkets, though none rivaled the battle my second wife and I witnessed in Rhode Island in the early 1980s. We came upon a woman and her young son, who was standing in the cart in front of the cereal section. The mother had refused to buy Count Chocula, so the boy screamed as loudly as he could, “I want everybody to know ... I’ve got the worst mother in the whole world!” True story.

BACK TO the leggy mother and the restless boy.

Another possibility is that I have lost the ability to control my facial expressions. Maybe my "been there, done that" smile seemed more like my infamous and condescending smirk, often interpreted as "I'm smarter than you," or (among men) "Your fly is unzipped."

Worse, maybe the woman thought I was leering. Possibly, I didn't hear her son tell her, "There's a man behind you, and he's staring."

I suppose I could have told her, “Your son is really cute.”

Except a comment like that from an old man raises red flags and cries of, “Security! Security!”

Of course, if I were a woman, and looked very grandmotherly, such a comment would be gratefully received, and given a reply: “Oh, yes, I think little Justin is really cute, too ... when he behaves.”

I WANTED to explain myself, but couldn’t do it honestly, because that would be an inappropriate and offensive thing for any man to say to a woman.

“Actually, lady, the reason I looked at you in the first place is you’ve got gorgeous legs.” Or I could have left no question about my age by referring to them as "gorgeous gams."

She might have had a gorgeous face, too, but while glaring, she reminded me of Cruella Deville.

A DISCONCERTING thing about aging is knowing — or, at least, assuming — how you appear to younger people. The ones who see you, that is.

That’s justice, I suppose, because knowledge is gained from experience, such as how older adults looked to us when we were in our teens and twenties. All I have to do is recall family reunions from the 1950s. Or, how old I thought my elementary school teachers were.

Inside my head, of course, I am much younger than my actual age. Most of the time I feel 55, with brief spurts all the way back to my youth. I assume this is true of everyone.

I’ve learned not to get carried away in such moments, not after what I did a few years ago, when the room over our garage was being converted into office space, and the outside stairs to the second floor weren’t quite finished. The bottom three steps hadn’t been put in place, but I was curious to see how the room was coming along, so I climbed up to the first finished step, and walked the rest of the way

Coming down, however, I suddenly felt 13, so instead of doing it safely when I reached the lowest step, which was about four feet in the air, I jumped — hit the ground, bounced forward, and landed on my face. I ached for days.

I hope to see that woman again. I don’t know if I'd approach her and offer an explanation, or stand at a safe distance and gaze at her. Probably the latter, because here in Land of the Shorts, I need to see more people for whom shorts were intended.

And looking at a woman's beautiful legs would be safer — and much less stressful — if I really were invisible.