I remember the first time I bought adult diapers, back when I was 20. I went to a little pharmacy. I was very nervous. They asked if they were for a senior, and I said "no." In hindsight, I think it was either just making conversation, or there may have been a discount to be applied. That was the most awkward diaper purchase I made.
Recently, I made three diaper purchases in one day. My first stop was a medical store, which disappointingly had regular Tena cloth-backed diapers as their best product. So I bought a pack, no questions. Then I went to a local pharmacy to buy some plastic Depends. Self-checkout, so no questions there. Then I went to another pharmacy, since I saw they had a few packs of the now defunct Depend Adjustable diapers on special. I bought those at the till, no questions.
It seems like if you go into a medical store and look comfortable, they just assume the products are part of your life somehow, and send you on your way. If you are nervous, you might be asked questions.