Last week I was automatically given the senior citizen discount at Dunkin’ Donuts. The teenage server behind the counter, in what I’m sure was an act of sincere generosity coupled with an even more sincere desire to keep the long line moving, didn’t ask whether I wanted it or whether I qualified. She just factored it in.

“Oh no!” shrieked a sensitive and impressionable younger friend, for whom, at 32, automatic senior citizenship seems like an impossibly distant and heartbreaking benchmark.

“But I saved 34 cents,” I replied. “That’s 34 cents I can put toward retirement.”

“But you’re not old enough to qualify for the D&D senior discount, are you?” she asks, eyes full of wonder. “You’re not even 60.”

Because she is a young person, however, I asked the following magical question: “How about if you look it up on your phone?”

Here’s what she found: After searching the Dunkin’ Donuts website, she located a deeply buried mention of “anywhere between 5 percent and 10 percent.”

I wasn’t satisfied. This is what happens as you get older: Certain details become increasingly important, and that’s why the word “curmudgeon” is rarely linked to the under-40 crowd.

As a favor, she found the number for our local D&D branch and I made a call – by this time we were back in my office. Curiously, my younger friend was vaguely appalled by this act because, apparently, nobody her age calls anybody anymore. She was engaged before she heard her boyfriend’s voice; I think they signed a lease together before hearing each other’s voices across a phone line. They text.

Anyway, when I reached a manager, I asked how old a person has to be to take advantage of Dunkin Donuts’ senior citizen’s discount. She replied offhand, “Oh, it’s, like, 50.”

I thanked her and called another D&D location a few miles away and was told the age was “around 60.” So I asked whether there was any way I could find out for sure.

Apparently annoyed, the associate with whom I was speaking requested that I “please hold” and covered the receiver with her hand. It was obvious that she asked the guy standing next to her what to do.

Their muffled conversation went something like this:

Girl: I have a lady who wants to know how old you have to be to get the discount.

Guy: The discount? For old people?

Girl: Yeah.

Guy: It’s, like, 65, isn’t it?

Girl: Yeah, but she wants to know for sure.

Guy: It’s 65.

Girl: No, I mean, she wants to know the real age.

The guy took the receiver. “Ma’am, it’s about 55.”

“So, there’s not a technical point at which a person qualifies?” I asked.

“It’s about 55. Or 65.”

“Ah. Thanks.” I left the conversation at that.

As you might imagine, this took quite a while. During this time, my younger friend had moved on, ended her engagement, got out of the lease and started a new relationship via Tinder.

Meanwhile, I’m there trying to figure out if I got my 34 cent discount under false pretenses.

Of course, what I was really trying to figure out is whether I look older than I am.

Finally I reached corporate headquarters where I was told that every D&D store is a franchise. Since they are separately owned and operated, each sets its own senior citizen threshold. Basically, it’s up to the discretion of the store manager. If the managers don’t set guidelines, it’s up to the cashier on duty.

Toward the end of my conversation, the woman at corporate headquarters announced cheerfully, “If you have an AARP card and buy a large or extra-large coffee, you know you get a free doughnut, right?”

Initially I’d been unnerved by the ridiculous fact that I might actually look my age.

But as soon as the corporate woman said the words “free doughnut,” all vanity was obliterated.

All I wanted was nine years’ worth of the sugar and fat I’d missed. That these are dietary items not scientifically proven to mitigate the signs of aging didn’t matter.

Like honey-glazed Rockettes, free doughnuts danced across my mind’s stage. They all looked around my age – and none the worse for it. If anything, they looked pretty sweet.

Gina Barreca is an English professor at the University of Connecticut and the author of “If You Lean In, Will Men Just Look Down Your Blouse?”