In my case, you find out that 80s teen star Debbie Gibson is affiliated with AARP.
You know you’re getting older when your birth year is near the bottom of the scroll-down menu.
In my case it’s being reminded that I’m technically old enough to be AARP spokesperson Debbie Gibson’s father.
Yeah, but you were back then, too.
Several years ago, I realized that I was old enough to be the mother of 3 presidential candidates (Swalwell, Buttigieg, and Gabbard). Granted, I would have been a mom of 17 or 18, but old enough nonetheless.
Even people known for certain to be legal adults (such as police officers) look like kids.
Your knees hurt and you’re not even using them.
I knew I was getting older when I happened to mention Carly Simon one day and my grown daughter said “Who’s Carly Simon?”
I know now that I’m old because I watch TV shows I loved in the '60s, '70s, and '80s and ask myself “Why did I ever like this crap?!?”
Technology which you still consider cutting-edge and use for pretty much everything (DVD player, DVR, tablet) is considered hopelessly outdated.
You remember a time when Star Wars was almost universally popular and nobody you knew saw it as anything but an exciting action-packed sci-fi adventure.
You don’t think pop music is any better or worse than it was 5, 10, or 20 years ago. It’s pop. What the hell does anyone expect, Beethoven?
Cartoons that you watched once, laughed at, and forgot about half an hour later as a kid are now the subject of lengthy point-by-point analyses on YouTube.
You still find it a refreshing change that sitcoms got rid of those annoying laugh tracks.
Your fears of Russian invasion did not involve any of the nations that actually bordered it.
None of the complaints you hear about Victoria’s Secret make any sense to you.
What is this nonsense? Surely almost everyone here is:
When you’re still sexually active and it’s as good as it ever was, some ways even better; but honestly: a good BM is a cherished joy.
I heard ages ago that the first sign of aging is when you notice how young all the cops are.
I didn’t understand it back then.
When JFK was elected my father mourned that for the first time the President was younger than he. I didn’t understand that either, then Obama came along…
You don’t remember “A Fifth of Beethoven”?
In my case, I knew I was old when I went out with a girl who was about my age, and she said, “Let me tell you about my grandchildren…” Gosh, am I that old? It took some doing, but I accepted that yes, I am that old.
I remember exactly this. I was pulled over, on the highway, in the middle of the night with my family sleeping in the car. The cop asked me, “Can I see your license, sir.” And I recalled that the previous time that I had spoken to a cop, aged about 18, his parting words had been, “OK, dickhead, fuck off.”
Assuming that, despite the passage of time, this cop’s attitude would be much like the previous cop’s, I didn’t point out my wry observation.
For me it’s always when X is young enough to be my child do I take notice. Police, teachers, doctors .
Doctor kind of stung
I’m a Great Uncle!
(Also I watched the first episode of Doctor Who and remember the Berlin Wall being built.)
I had a startling moment one Sunday when I was watching an NFL game and realized I was older than all the players on the field.
And another startling moment a few years later when I realized I was old enough to be the father of any current player.
…when the subject old lady of the OP is 10 years younger than you.
But you fell young again when you realize you don’t look as old as she does.
First, high school girls started calling me “sir”. 
Then, college girls started doing it. 
Now, cops and doctors are starting to do it. 
Colonoscopies.
Prostate exams.
It’s too bad I’m straight.
The young guys I play music with are in their 50s.