peacenlovealways said:

I HATE when people do that! I remember once at a company function, I did not take anything from the buffet, because I was not hungry. A co-worker asked me, "Do you have an eating disorder?" I wanted to say, "No, I don't, but even if I did, that is none of your business!" I was nice to her, and said that I didn't, and that I was not eating because I was not hungry. But really, I wanted to get nasty with her. People need to keep comments like that to them damn selves.

I had my daughter at age 40 and I am not so happy that people either ask me if she is my grandedaughter or tell me she is; as in, "your grandedaughter is so pretty".
Why not assume that an older woman is with her daughter? If you are wrong she may feel complimented.