"Young lady" is both condescending AND patronizing. The correct form of address would be Miss (for a young girl or teen), Ma'am for an adult or the person's name with the appropriate salutation. How would you have felt if she replied, "Well, I'm not sure, Old Man, let me try to recall what happened that day."
I'm rarely a stickler for these kinds of things, but remember when I was in my late 40s and making a deposit at the bank branch I'd used for years. There was a new, very young teller who asked for my ID, then a second ID, both of which she scrutinized closely before proceeding with my transaction. At the end of the transaction she breezily said, "Thank you, StarSong," having gleaned my first name during the transaction.
I was a bit irritated by then at the amount of time this simple deposit had taken- and was so shocked by her sudden familiarity that I let loose with, "Please don't address me by my first name. You OBVIOUSLY don't know me and we're not friends." Poor girl was stunned. I doubt she had to learn that lesson twice.
My kids happened to be with me and were a bit shocked by my out-of-character reaction. I told that when working in retail it is appropriate to address customers as Sir or Ma'am unless invited to do otherwise, particularly if they are much older than you, it's the first time you've dealt with them, and you just spent a great deal of time checking their IDs.