Old Dave

Yesterday our scheduling was a bit off, we only had one mainline cashier for 4 hours in the morning - when that happens either my mid-head cashier or I will open up a register.  Yesterday morning we switched off, he spent time checking out customers and then I would do a 30 minute shift.  We are always prompted to ask if the customer is going to put their purchase on a store credit - always.  So I asked this customer and his response was, "no, old Dave," (we have our names on our aprons).  My response was "well, I'm not really that old," and he actually said "well, you evidently didn't look in the mirror this morning before you left the house."
Is that an insult or not?
Now I could have been a smart ass, but I need to be kind - customer service you know?  So, I overlooked his ignorance figuring he was probably a Trumplodite.  Why would you even say something like that to a stranger?  Call them old?  I'm not as young as this guy was (probably mid-30's) and I'm not as old as my Mom (she's 83). True, I suppose I could be classified as an 'early senior.'  I'm too young to retire.  But I wouldn't qualify myself as being old.

And though I may have looked like this in my youth, I didn't pose for the sculptor

I'm not easily offended, so this guy didn't offend me.  I suspect this may have been his way of making a joke.  Or perhaps in his ignorance he called everybody older than himself 'old.'  The most perplexing thing for me, however, was that he said anything at all. Maybe I'm finding this so confusing because I really am 'old Dave,' or it could be I just don't want to admit to myself there really are utter assholes like this guy in the world.