What an idiot!
On this board, we collectively should be able to come up with a good comeback for something like that...
Maybe "No, I wasn't a teen mom but thanks for asking..."? Although I have nothing personally against teen moms. Anyone have a better comeback?
I would be annoyed too but no reason to call into question other moms. There's a lot in between "older mom" and teen mom. I was a teen mom (18) and now I'm about to have a baby at 35, so not as young.
I would just correct the person and move on. They will probably feel stupid enough when they realize what they said and that they were wrong.
I think people should just assume it's the parent until you are told differently. Much better to assume it's the mother and be told it's the grandmother than to have the opposite.
EDIT I just wanted to add I am dreading this. I was talking about it with my sister the other day. I hate that people need to speak up at all. I hated the judgement I faced as a young mom and I am dreading the comments on the way now.