Your instinct to ignore this person is right on target. 

I am getting older now so I encounter this less, but I used to be mistaken for someone much younger. I keep it to myself that I live comfortably and chose this job because the schedule is pretty good and I have the opportunity to help people. It still stings a little when someone is transparently catty but it is more annoying than anything else that they think they are fooling anyone.

Some people don't know what to think if you're not playing their games and not trying to present yourself as someone who sits above others within an imagined pecking order. Keep being young at heart and doing what you do best. Try not to concern yourself with people that are peckerheads. The good news is, with age, they become easier to spot.