This would be incredibly rude, to me.

That is the time and place to place a solemn curse on the utterer condemning her to live to be 95 and have to interact with high school students every day after she turns 40.

This happened to me once - and I was only 32 at the time. The offensive person was a teenager at the time and, I would say, not the brightest candle on the cake. She blurted it out when I mentioned the year of my birth. I responded by saying well, I did say 19** not 18**. I thought it was kind of funny at the time...on some level, I think I still would if it happened today.