It all depends, really, and big box stores seem to be more apt to card me than mom-and-pop shops.
In Pennsylvania, at least the big grocery stores, actually scan the bar code on the back of my driver’s license to read in my info and release the purchase.
Here in Ohio, they generally just look at me, override the sale, and put in a fake birthday, like 01/01/1950, and send me on my way, though I’ve had a couple of jerks not sell me beer because I don’t typically have my ID on my person. One of the few times I (nearly) made a big grocery purchase at Walmart, I left it half scanned through, half in the cart, a good $200 worth of things, because the stupid cashier insisted on carding me, grey beard and all, and when I walked over to customer service to complain, the manager said, “Yeah, I obviously wouldn’t card you, but it’s up to the cashier,” so that was that. Letter of the law destroying spirit of the law, IMO.
Years and years ago, MrsT and I were working an Oktoberfest, and our job was to card anyone at the gate wanting to buy alcohol and give them a “It’s ok, I’m a grown-up” wristband, and the state police had insisted on 100% compliance, so we were expected to card 80 year-olds and the like, and we, being in possession of some

common sense, refused and so they took us off the wristband patrol.