I'm over sixty. When I buy ammo at Wal-Mart, I still get asked that question.
Typically the ammo in question is 9mm Luger.
There I stand, gray hair and all, and the clerk -- who is himself over fifty -- looks up from the register and says, "is this for rifle or pistol?" and then checks himself with a grin.
My standard answer when they do that, is to say, "oh, it's for my Marlin Camp 9." I pretty much always get a squint, then I tell the guy it's a carbine, and get a bemused, "oh, okay." I've had a couple of clerks who actually knew what the Camp 9 is.
Every so often I'll say it's for my Beretta CX-4. Never yet had a clerk recognize that. "It's a home defense carbiine." . . . "Really?" . . . "Yes indeed; you've never seen one? I can bring it in if you'd like."
I've offered to bring in the carbine on a half dozen occasions. Nobody has ever taken me up on it. Makes them nervous for some reason.
I generally get along well with the Wal-Mart sporting goods counter folks. I yank their chain a little when they get too stiff, but that privilege kinda comes with age.
Probably my most fun ammo buy at a Wal-Mart was when I bought a rifle in Reno, and the lady overseeing the purchase was recent transfer from someplace back east. I was about to wrap up the sale and said, "and I'll take a couple of bricks of that Federal over there." You would have thought I'd asked for her daughter's phone number. Complete indignation. "Sir, we cannot sell you ammunition with a gun." I was genuinely stumped. "So, I can put the rifle in the truck, come back into the store, and buy the ammo on a separate ticket, but we can't do that on the same receipt??" Fortunately, a more seasoned manager was handy, and he explained to her, "I don't know how they did it where you came from, but this is Nevada, and we can sell anything he wants on that same ticket."
Don't take it personally.
The laws are bad enough at the federal level, but then each state gets to add its own little variations.
Add to that the fact that nationally distributed stores often have to adopt lowest-common-denominator policies across their chain of locations in order to have some kind of uniformity in their training.
And, in exchange for some occasionally stoopid rools, and random robotic interpretations, it's possible to get ammo at a significantly reduced price.
Remember, don't hate: robots are people, too.