...it did seem like the kind of assumption we're talking about here.
I have check-ups at a medical facility which, if you looked it up in the phone book, or saw a brochure about it, would be described as pediatric. They follow me for a problem I've had since birth, since there really aren't many doctors who treat this problem just in adults (at least, not everywhere, not yet.)
Well, during one of my appointments during one of the years I was in my graduate program, a hospital social worker came to introduce herself and asked me, "What grade are you in?" I set her straight, straight-forwardly.
The main doctor who sees me has assured me I'm not even his oldest patient. I wasn't so much mad at her, but upset at the idea that I seemed so much younger (part of the reason has to do with some of the effects of the medical problem itself.)