Age is a number. One we cannot control. But we are only as old as we behave. Or are able to behave.
The standard line about “… only as old as you feel” is an invitation to delusional thinking. If you can walk the walk, you’re young no matter when your original birthday was. If you can only talk the talk, or have forgotten what the talk is, then you’re old, no matter your age.
Happened to me just a few days ago. Patiently waiting to get a bottle of scotch and the attendant showed up and the other guy (around 40) said “This young man was first.” (I’m 63). I’m a good looking 63, but I’m not a young man. I never felt so old.
It grates on me, too. It’s condescending, dismissive of an old person’s lived experience, assumes the target wants to deny the reality of their age. Especially when said of/to an old women, I get undertones of the target being expected to simper gormlessly at the supposed gallantry.
Yes! condescending on steroids! Never mind getting off my lawn, anyone who tried that on me would be likely to wind up six feet under the grass.
ETA: Procrustus is spot on.
“How old would you be if you didn’t know how old you were?” - Satchel Paige
“I wouldn’t know.”
If Willard Scott didn’t invent that one, he infringed on the copyright VERY egregiously! I’m curious why the OP is set off by this instead of “I was today years old when I found out…”
I fail to see what is possibly objectionable about that. At that age there are big differences between 2, 2 1/2, and 3.
Same sentiment expressed by Toby Keith in his song “Don’t Let the Old Man In”:
Many moons I have lived
My body’s weathered and worn
Ask yourself how old you’d be
If you didn’t know the day you were born
From the Clint Eastwood production The Mule (2018), a melancholy self-reflection on aging.
I’m with you. I didn’t read the pitting but what is wrong with it?
I took it to mean she was called half a person; 2 adults and a child enter the restaurant and are referred to as 2 1/2.
One of the docs I work with always asks ‘how many years young are we?’ Which is double irritating for me, as I’m not fond of ‘what are we having, what are we thinking, etc’ either.
I called my ex-wife “Babe” often. Or “Luv.” She had a three-syllable name that she did not like shortened (it wasn’t her name, but think “Stephanie” becoming “Steph” or “Fanny”; she preferred the full “Stephanie”), so Babe or Luv worked in such situations, and she was fine with those. “Hey, Babe, I’m going down to the corner store. Do we need anything?” “Hello, Luv, it’s me. Will your flight be on time so I know when to go to the airport?”
As for, “years young,” it’s no big deal. On the nightly news, if a local centeniarian is presented as, “Margaret Smith, who is 100 years young today,” I don’t care. Good for Ms. Smith for reaching such a milestone. Like I said, it’s no big deal to me.
OMG - I hate this with a white-hot hatred that cannot be un-hotted! Young lady is reserved for scolding a sassy little girl who needs to be put in her place! 
Similarly, those who, hearing it’s my birthday, feel compelled to say “29, eh?” or something equally inane. You don’t flatter me with such stupidity. I hated it when I was 50 and I continue to hate it into my 70s. I’ve never pretended to be other than the age I am. OK, I may not always act it, but I also don’t respond to “How old are you?” with “How old do you think I am?” < deep cleansing breath > Yeah, it pushes my buttons…
I fully support the OP on this pitting.
But even more grating, to my ears, is this:
mmm
I define “Old” as “15 years more than my current age”, it used to be “20 years”, which is worrying…
Eh, my description was incomplete. As @outlierrn noted, they were calling her half a person, which I found objectionable. There are three of us needing to be sat, not two and a half.
Ah I see! Yeah that’s an odd usage.
I can remember ‘half’ birthdays being a very, very big deal to me as a child. Six-and-a-half was closer to being with the big kids; six was closer to being with the babies (or, as my mom’s side of the family says, “the littles,” which absolutely makes my teeth itch for some reason.) But yeah, I do understand the context of that particular rant.
I’ve never liked it when people make a big deal about being carded. “Oooooo, they think you look so young!!!” No, they’re asking for my ID because they’ll get reprimanded or fired if they don’t. The whole carding thing is also a bit of a sticking point for me because at the time I turned 21 my state was still using distinctly colored photo backgrounds to indicate if a person was of age or not. But my license wasn’t up for renewal when I turned 21, so my photo still had the ‘underage’ background; when I would try to order a drink, most servers would take one look and decline it, completely ignoring the printed date.
There was a popular long running sit-com that used it.
I’m 77 (how did that happen?), but most of the time I don’t feel ‘old’. I still enjoy learning about any variety of new things, write and record songs, etc… can crank up college calculus to solve problems if needed…
I’m lucky that I don’t have any disabilities or chronic illnesses… yet. Don’t need a stick or other walking aids etc. The only real change is I don’t have the stamina I used to: in younger days I hiked all over the Snowdonia mountains… not so much nowadays, alas.
I’m not ‘letting the old man in’ as long as I can avoid it!
But I am sure as hell not ‘77 years young’ 
I used to be with ‘it’, but then they changed what ‘it’ was. Now what I’m with isn’t ‘it’ anymore and what’s ‘it’ seems weird and scary. It’ll happen to you!